Maupas_1900

The tail (pl. XXIV, fig. 6) is short; its free extremity is thick and rounded, and still almost half as wide as its origin. Towards the middle of its length, it bears a pair of lateral papillae, which are extremely fine and difficult to see. One can only succeed in seeing them on individuals that lie on the ventral side and are rather strongly compressed.

In well-fed individuals, the cells of the intestine are filled with albumino-fatty granulations, which accumulate as storage substances. These granulations also invade all the connective tissue in the walls along the esophagus and inside the tail. They give a general opaque aspect to the body. Birefringent corpuscles are never found.

The nerve ring (pl. XXIV, fig. 5 c), of fibrous structure, is seen with some difficulty. It envelops the esophagus neck at its anterior extremity and bends obliquely towards the ventral side, extending out towards the excretory pore.

The excretory apparatus (pl. XXIV, fig. 5 p) is difficult to observe. The small unpaired chitinized tube can be seen relatively easily. It first describes a narrow and long loop directed towards the front, then folds back towards the bulb. The pore is located slightly in front of the bulb. The lateral canals can only be observed on emaciated and strongly compressed individuals. I did not succeed in following them beyond the vulva. A unicellular gland is found close to and behind the pore.

The vulva (pl. XXIV, fig. 3 v) is located at the boundary between the second and third thirds of the total body length. Its lips are slightly swollen. The vagina is very short. The genital tube is unpaired, with a relatively long uterus. Taking the shape of a narrow sac, it extends directly in front of the vulva and finishes in a dead

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end. It never contains more than one egg, always laid before the arrival of the next. Behind the vulva is found an aborted genital tube in shape of a narrow transparent sac, of a length equal to two and a half times the body width. The uterus connects to the ovary through a narrow oviduct inserted at the end of the second third of its length. The ovary comes back down directly along the body and ends slightly in front of the extremity of the intestine. In the middle, between this extremity and the vulva, it always forms a rather long double loop.

The eggs (pl. XXIV, fig. 7), of oblong shape rounded at the extremities, measure 66 μ in length and 26 in width. Their chitinous shell is shagreened (covered by small protuberances). The vitellus is colored in dark mahogany brown.

The multiplication of this Cephalobus takes place very slowly. The layings occur at a great interval from each other, with a maximum of 8 to 9 per 24 hours, at a temperature of 26 to 27° C. Only a single egg can ever be seen in the uterus. These eggs are always laid before their first cleavage. The species is thus essentially oviparous.

The development and the growth are very slow; however its lifespan is quite long. At a temperature of 26 to 27° C., the eggs take 4 days 1/4 to develop from laying to hatching and the larvae 16 days to reach a perfect adult state and lay their first egg. Here is actually the complete history of a female, which I followed day after day from its origin until its death of old age. It came from an egg that was laid on July 29 and hatched on August 2 in the evening. It grew until August 17, when it did its first laying. The layings continued until October 5, and from this day, it lived fully sterile to perish of senile exhaustion on November 14. During the fertile period of 49 days, the daily number of eggs was quite variable and never exceeded 9. The

total of the layings was of 315 eggs. This female had lived for a total of 105 days.

The juveniles coming out of the egg (pl. XXIV, fig. 8) are all born with their complete organs, except for the genital apparatus which is still in an extremely rudimentary state. But the proportions of the parts of the body are very different from those of the adult state. Indeed, the esophagus and the tail equal 1/2.6 and 1/16 of the total length, respectively, instead of 1/4 and 1/19. It results thereof that, in the final growth, the greatest part is contributed by the middle region of the body, which multiplies 4.5-fold, whereas the esophagus and the tail only multiply 2 and 2.5-fold.

This species suffers long dessications with impunity and revives as soon as it is moistened again. I have seen some regain life in a few hours, which were dessicated for five years. In my cultures, I fed it with diluted rotten flesh.

The movements are slow and heavy.

Cephalobus lentus is a species with a parthenogenetic reproduction. I made sure of it:

1° By ascertaining the absolute absence of males;

2° By rearing juveniles and following them until the adult state; all became females, which laid eggs that developed regularly;

3° By examining at high magnification the genital organs of the adult females, and not ever seeing the least trace of spermatozoa;

4° By observing, in an immobilized individual, the arrival of an egg into the uterus and following it after its laying until the first division into two blastomeres. I repeated this observation several times, and during its whole length never saw two distinct pronuclei, nor their coming together and their mating, phenomena that are so easy to follow in the dioic or hermaphroditic species.

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PLECTUS CIRRATUS Bast.

BASTIAN. – Monograph on the Anguillulidae, 1865, p. 119, pl. X, fig. 81, 82.

DE MAN. – Die frei….. Nematoden der niederländischen Fauna, 1884, p. 110, pl. XVII, fig. 68.

I found this species twice in Algeria; a first time in humus that was sampled by M. Ficheur, at an altitude of 1,500 meters, on the Southern slope of the Jurjura; a second time in the meadows of Maison-Carrée, close to Algiers. I cultured it on depression slides, by feeding it with diluted rotten flesh.

The drawings and the description of De Man being very sufficient, I will satisfy myself with presenting the observations that I could gather on the biology and sexuality of this nematode.

Growth and multiplication are not very rapid. At a temperature of 26° C., the eggs take 44 hours to undergo their embryogenesis until hatching. At the same temperature, the larvae require 10 days to grow until the adult state and the laying of their first egg. Still at the same temperature, it lays a maximum of 30 eggs per day. I did not make any observations on the total number of its eggs, nor on its lifespan.

This species is essentially oviparous. It lays its eggs most usually before the first cleavage. Therefore no more than 5 to 6 eggs can ever be seen together in each uterus.

The maturation of its eggs is interesting to follow. When the ova of the anterior region of the ovary are mature and ready to enter the oviduct to pass into the uterus, they display a very conspicuous and large germinal vesicle, of slightly elongated shape, measuring 12 to

13 μ, and endowed with a large spherical nucleolus, measuring 5 to 6 μ. They cross the narrow strait of the oviduct by stretching and fall into the uterus, where they curl back on themselves and take a slightly irregular shape, but close to the spherical state.

At the time of passage in the oviduct (tuba), the germinal vesicle is still intact, with the abovementioned dimensions and thus still very conspicuous. But as soon as the ovum has entered the uterus, the vesicle undergoes a deep change that renders it almost invisible. On some eggs where it is most likely located at the bottom, it can be searched in vain. On the others, where it is located on top, one can recognize it under the aspect of a diffuse spot, of circular shape and half as big as the primitive vesicle.

The eggs stay in this state in the uterus for half an hour to three quarters of an hour (temperature 27 ° C.) and wrap themselves in their shell, which is covered with small spikes.

I examined at high magnification a great number of these uterine eggs, and always, without a single exception, I saw them having a single nuclear spot. This observation is important for the demonstration of their parthenogenetic state. Indeed, if this nematode had been hermaphroditic and its eggs had been fertilized, I should certainly have come across one of these eggs with two yet unfused pronuclei, as can be easily seen in the dioic or hermaphroditic species.

After about three quarters of an hour in the uterus, the eggs are laid with a well-formed shell. At the very moment of their laying, the vitellus fills out the whole cavity of the shell without letting any empty space. At the same time, the nucleus or germinal vesicle has become completely invisible. It is probable that this invisibility is

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caused by the labor of production of the polar body, which I actually never could see in any egg.

This invisibility lasts for approximately one hour to one and a half hour; then the nucleus reappears under the form of a beautiful clear nucleolated vesicle, of the same dimension as the primitive germinal vesicle.

At the same time, the vitellus retracts, letting rather large empty spaces in the cavity of the shell, and is agitated by amoeboid movements, which are clearly visible with the eye and which drag the nucleus sometimes on one side, sometimes on the other. This state lasts approximately for one and a half hour, then comes the cleavage into two blastomeres. The two first blastomeres are still endowed with amoeboid movements; but I did not observe any at the stage of four blastomeres, which occurs approximately one hour after the first division (temperature 27° C.).

This maturation and this laying are perfectly identical to that observed and described in the Cephalobus dubius.

Above, we stated the parthenogenetic state of this Plectus by basing us on the mode of maturation of its eggs. To this demonstration, we can add the followings:

I observed many individuals, without ever encountering a male. I reared juveniles that had been isolated since the time of their hatching, and all became females that laid regularly developing eggs. These fertile females could have been hermaphrodites.

I had more difficulties to ascertain directly the absence of hermaphroditism. The organ of reproduction is rather difficult to see in its entirety; especially in the upper region of the uterus, where it narrows into an oviduct (tuba), which folds back underneath and inside to connect to the anterior part of the ovary. But by

appropriately compressing live individuals, I could ascertain many times the complete absence of spermatozoa in the entirety of the uteri and oviducts of females that were laying regularly developing eggs.

I moreover took young females reaching the adult age, but without yet a single egg in the uterus. At this time, in the hermaphroditic species, one can witness the formation of sperm in the upper region of the ovary and its storage in a receptacle. The last germinal cells in this ovary region take the shape and development of spermatoblasts, which are always smaller than the mature ova ready to enter the uterus. In the Plectus, I never saw spermatoblasts, but always ova.

Finally, by cutting adult females in two with a fine blade, either in pure water, or in 1 % acetic acid, one can almost always obtain the hernia of an ovary and of its uterus, which then become easy to observe in their entirety. I did not see therein any trace of a seminal receptacle nor of sperm.

I brought the greatest care to these verifications, because of an anatomical particularity of the oviduct, which troubled me for a long time by making me believe in the possibility of hermaphroditism. The uterus of this Plectus and the oviduct are composed, like the intestine, of small polygonal cells without apparent nucleus. In the region where the oviduct and the uterus meet, one or two of these cells often contain small opaque corpuscles (pl. XXV, fig. 1 c c), of spherical shape, that simulate rather well spermatozoa of very small size. But, as I said above, I could never see the spermatoblasts of these pseudo-spermatozoa. Moreover, their number was very insufficient to account for the fertilization of the many laid eggs of each female. Finally, I often searched for them in vain in young

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females that had already their first egg in the uterus. These corpuscles cannot have anything in common with spermatozoa.

De Man states the existence of males and gives their description. He adds that they are extremely rare, wheras the females are very common. Bastian, like myself, has not seen any male. If the observation of De Man is exact, we would have in this Plectus a parthenogenetic species, in which the male sex would sometimes reappear as an atavistic sign of an ancient dioic state.

APHELENCHUS AGRICOLA DE MAN

BÜTSCHLI. – (Aphelenchus avenae). Beiträge, etc. 1873, p. 46, pl. III, fig. 15.

DE MAN. – Die Nematode, etc., 1884, p. 138, pl. XXI, fig. 90.

I found this species twice in Algeria, the first time in soil coming from the region of Bousaada, the second time in soil sampled on the ridge of the forest of Teniet-el-Hâd. Bütschli encountered it in Germany and de Man in the dunes of Holland. It lives in light, more or less sandy soils, among plant roots.

Measurements:

The rather thin body (pl. XXV, fig. 2) of uniform diameter tapers slightly and gradually in the esophagus region to end by the truncation of the mouth; its posterior extremity is rounded. Its general aspect in well-fed individuals is rather opaque; opacity that

is caused by the many granulations stored in the walls of the intestine.

The cuticle is finely transversally striated. The lateral membranes have the shape of two bands of a width larger than the body diameter by more than one third. These bands bear 10 to 12 fine longitudinal striations (pl. XXV, fig. 5 m). The transversal striation stops right at the edge of these bands. They maintain their width from the extremity of the tail until beyond the esophagus bulb, then narrow rapidly and end by completely disappearing in the buccal region. De Man described these striated bands very well; but he confuses them wrongly with the lateral fields that are found below and which belong to the muscular-cutaneous layer and not to the cuticle.

The mouth (pl. XXV, fig. 3) ends the anterior extremity without any special change that would separate it from the rest of the body. The cuticle is only thinner and without striations in a small zone. There are no lips, nor papillae. The stylet of the buccal cavity is clearly tubular and its walls continue without discontinuity with the chitinous tube of the esophagus. There is simply a slight thickening at their junction point. Another much smaller thickening is also found in the middle of its length.

The esophagus (pl. XXV, fig. 4) presents the usual conformation for Aphelenchus. The bulb is powerful and with a clearly fibrous structure. It always contains two to three finely granular masses, of glandular appearance. Its internal chitinous wall is strongly thickened. The part of the alimentary canal that follows, the substance of which is always clearer and without granulations, represents for me the second part of the esophagus, as known in the neighboring genus Tylenchus. In most Aphelenchus, this clear part