60 ENTOZOA. 



production, not only in distinct genera but even in species — at least, 

 this appears to be the case, if the facts recorded by authorities are 

 trustworthy. In the situation referred to, the first formed germ- 

 ceUs display two or more nuclei within, and these rapidly multiply 

 as development advances. By and by the nuclei enlarge and 

 project from the parent germs, ultimately forming semi-independent 

 secondary germs, or, more correctly, unimpregnated primitive ova. 

 The original parent germ now becomes a bond of union between 

 the quickly enlarging primitive ova, constituting, in fact, the rachis 

 of Dujardin. Each primitive ovum now acquires a more or less 

 pyriform shape, being connected to the rachis by a narrow peduncle, 

 and one entire group of such ova assumes the aspect of a botryoidal 

 cluster, or so-called egg-raceme. At a further stage, when the 

 primitive ova are ready for impregnation, they separate, according 

 to Meissner, from the rachis, and the fractured surface of the 

 ovum where it joined the pedicle becomes the micropyle aperture. 

 This opening is supposed by Meissner to give admission to the 

 spermatozoa of the male, and the consequent admixture of the 

 latter with the yolk granules of the primitive ova constitutes the 

 very act of impregnation. After this act the germinal vesicle of 

 the primitive ovum disappears, and the process of yolk segmentation 

 soon commences, which, of course, speedily determines the formation 

 of the embryo. 



As before hinted, the details of this process in Mermis are some- 

 what peculiar, and they differ remarkably from what has been observed 

 by Nelson, Thomson, and others, in Ascaris, and by Lubbock in the 

 more closely allied genus Sphaerularia. In this place, however, I 

 must leave the consideration of the mode of egg-development, in so far 

 as it concerns the genus Mermis, and reserve my necessarily brief 

 notice of the controverted poiats as regards the egg-development of 

 other Nematodes for separate treatment. Meanwhile, I have to re- 

 mark, that at or near the time of the maturation of the ova of Mer- 

 mis, the parent worm, hitherto lodged within the body of some insect, 

 seeks to bury itself in the soil, and it accomplishes this wandering 



