In fact, the interior of the body is wholly occupied by two relatively enormous organs—the double series of secretory cells, and the ovary.
The former of these extends in a straight line from one end of the body to the other, being attached at the extremities, but otherwise lying loose in the interior. The cells lie side by side, and thus form a double series. Some of them are very large indeed, being even as much as 111th of an inch in length by 133rd in breadth. Others, however, are not above half as long, though they do not differ much in width. They are not arranged with any regularity as to size, so that often a long one lies by a short one, in which case, however, there is no gap; but the series becomes more or less alternate, until, perhaps, another difference brings each two cells again nearly opposite to one another.
Each of the large cells contains a thick fluid, and about seven or eight transparent nuclei, which are of tolerably even size, and about 81000th of an inch in diameter.
A very similar organ to this has been described by Meissner in Mermis albicans, where also it consists of a double series of large cells, with nuclei. The large cells, however, are full of oil globules, and the nuclei contain crystals. In Mermis nigrescens and in Gordius the fat-body consists of a large number of much smaller cells. In the last-named genera this fat body is continuous, with a very short œsophagus; and I have therefore examined the two ends of it, to see whether the same was true for Sphærularia. I never, however, found anything in the least like the narrow œsophagus and peculiar stomachal sacs of Mermis, nor the small mouth and short œsophagus of Gordius. It seems, however, that this corpus adiposum must be considered as homologous with the intestine of the Nematodes, although no central cavity has been formed in it.
The ovary is about four inches and a half in length ; it commences near one end of the body, as a fine tube about 11000th of an inch in diameter, and gradually increases to about 1120th, after which it slightly diminishes, then again expands into an uterus 140th in diameter, and then finally contracts to about 190th, and opens externally at the extremity of the other end of the body. It lies perfectly free in the general cavity, but near the vulva is connected with the large fat-cells. The female generative organs of Sphærularia differ therefore considerably from those of Mermis and Gordius, both of which have a double ovary connected with the vulva by a short oviduct.
According to Claparède,[1] in all Nematoidea, the Purkinjean vesicle is the first-formed part of the egg:—
"Il parait certain," he says, "que chez tous les Nematoides la vésicule germinative est l'élément primaire de l'œuf. Le blastogene n'ayant chez l'Ascaris mucronata qu'une largeur d'environ m, 013, ne peut comprendre plus que deux vésicules germinatives dans sa largeur. Ces vesicules s'entourent d'une mince couche d'une substance glutineuse et incolore. C'est là le premier rudiment du vitellus. Nous n'avons pas rencontré d'individus chez lesquels les œufs eussent atteint un developpement plus considérable."
- ↑ De la Formation et de la Fecondation des Œufs chez les Vers Nématodes, p. 38.
