CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 113 

 EMBRYOGENY AND DEVELOPMENT. 



It lias already been stated that the uariow terminal extremity of the 

 ovary is filled with a finely granular, amorphous, opaque, and homoge. 

 neous substance. On approaching- the coiled portion of the ovary this 

 granular matter is seen to unite into spherules, which are the ovules 

 proper. They are ranged in a siugle row ow ing to the narrow tube, the 

 internal diameter of which they almost fidi up. In the wider portion of 

 the ovary they range themselves in two or three rows. Near the ovi- 

 duct (Fallopian tube) they first become slightly ovoid, with a long di- 

 ameter of .08""°' (.003 inch), and they possess a distinct germinal spot 

 and vesicle. Still without shell or distinct enveloi)e, they are led, one 

 by one, through the oviduct into the corresponding uterine horn, where 

 they find themselves in contact with the spermatozoids, and where they 

 become inclosed in a shell. When this is completed, and the egg con- 

 sequently perfect, it presents the form of an ellipsoid, with a long di- 

 ameter of .09"'"' (.0035 inch) and a short one of .05""" (.002 inch). The 

 egg is not truncated nor provided with a neck at each extremity, as is 

 the case with many nematodes. There is, on the contrary, at each pole 

 a thickening, hemispherical externally and almost flat within (Plate II, 

 Fig. S, A, B, C). Tnis is an actual cover, detaching itself completely 

 when the embryo emerges. Only the empty ovum, therefore, is really 

 truncated at its two extremities. 



In the uterine horns the ova undergo complete segmentation. Their 

 vitellus divides into 2, 4, 8, 16, &c., small spheres, which assume the 

 mulberry form (Plate II, Fig. 8, A). The development proceeds in the 

 lateral regions of the egg (Plate II, Fig. 8, B), and at its close the 

 embryo may be seen rolled up in the foi m of a circle or a figure of eight. 

 The egg is now .1""" (.004 inch) long and .06'"'" (.0024 inch) broad. 



But it is not to be supposed that all the developmental phases of the 

 ovum can be followed out in every syngame. Only in case of the 

 largest specimens can this be done by examining successively the genital 

 organs of the female, from the extriMuity of the ovaries to the body of 

 the uterus after they have been taken from the body and well spread 

 out. It is also possible to trace the series of successive transformations 

 which the ovule undergoes from the embryonic to the perfect state by 

 examining a series of females from the moment of their sexual union 

 with the male to that of their greatest development. Thus in the syn- 

 games recently conjugated, at a time when the female is scarcely 5™"^ 

 (.2 inch) long, only spheroidal ovules are found in the uterus and its 

 appendages, which are verj* short, but slightly developed, and not dis- 

 tinct from the ovaries, their diameters being the same. When the 

 femah' has reached a length of 1'""' (.4 inch), the uterus and its horns, 

 now (juite distinct, contain eggs fully formed and inclosed in a shell , 

 but the vitellus is not yet segmented. When the body is 15"'"' (.51) 

 inch) long the vitellus is already segmented, and has even passed 

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