LT7SB0CK ON SPH^HULASIA B0M3T. 49 



Leuokart, also, expresses himself in a very similar manner. Meissner, 

 however, as is well known, has given a different, and very remarkable 

 acconnt of the development of the eggs in Mermis. According to him, 

 the eggs commence as a cell with a nucleus; the nucleus divides, and 

 the new nuclei become the germinal vesicles, while the old cell- wall is 

 gradually produced into follicles, into each one of which a germinal ve- 

 sicle enters. Finall}*, the follicles are, by gradual constriction, separated 

 from one another ; and in this manner a whole festoon of egg?, besides 

 several abortive follicles, originate directly from the moditication of a 

 single cell. 



Sphaerularia offers so many points of agreement with Mermis, that 

 the development of the eggs naturally became specially interesting ; and 

 although my observations are very incomplete, I can ac least say, that, 

 if the account given by Meissner is correct, there is in this respect, at 

 least, no similarity between the two genera. 



At the extreme end of the ovary I found a large cell with a nucleus. 

 Following this cell are a great number of small vesicles, which much 

 resemble true nucleated cells. They occupy the whole cavity of the 

 ovary, and each of them is about g^o-th of an inch in diameter. These 

 are at iirst transparent, but gradually become more and more opaque on 

 their inner side, from the deposition of minute yolk globules. The Pur- 

 kinjean vesicle is also distinctly visible, but I could see no macula. As 

 the ovary widens, the eggs gradually become wedge-shaped, the outer, 

 larger portion remaining clear, so that in this part of the ovary there is 

 a transparent border, with an opaque central axis. This axis, which is 

 known under the name of "rachis," becomes gradually smaller and 

 smaller, being absorbed into the growing egg, which becomes more 

 and more opaque, and assumes a ronnd shape, the Purkinjean vesicle 

 remaining for some time visible in it, and containing a single macula. 



"When, however, it has entered the wide part of the tube, which we 

 may probably call the uterus, it has again become' elongated, and has 

 lost the Purkinjean vesicle, and the yolk has begun to undergo segmen- 

 tation. PL I.,/ 11, represents a very common state of the egg at the 

 beginning of this process: the first two yolk-spheres, each with its nucleus, 

 lie at the two extremities of the egg; and the central part is occupied by 

 a mass of yolk, divided into an uncertain number of irregular masses, 

 which however contain no nuclei, and are not regular spheres of seg- 

 mentation. Farther down the uterus we find eggs in all stages of seg- 

 mentation (PI. I.,/. 13); and in several instances I could distinctly 

 see the nucleus dividing, as in PI. I.,/. 12, in preparation for the next 

 division of the yolk. The segmentation is already far advanced when 

 the egg is laid, but I never found in the uterus any eggs with a fully de^ 

 veloped embryo. 



I noticed a few specimens in which all the eggs near the vulva were 

 broken up into irregular masses, and in one specimen this was even car- 

 ried so far, that it began when the eggs were onty about half grown. 

 In normal eggs, the development of the young takes place in the man- 

 ner usual among Nematoids. 



VOL. I. N. H. E. H 



