290 ANIMAL PAltASITES. 



times in the lowest portion of the latter, the eggs, already 

 fertilized and in progress of development, are pressed extremely 

 closelv, one behind the other, the germinal vesicles make their 

 appearance in the middle, and as the}' all lie in the middle, they 

 acquire the appearance of a string of figs, or still better, that of seg- 

 ments of Bothriocephali. At the point of transition of the narrow 

 tuba we see a peculiar sphincter. 



5. The Uterus. — It exhibits externally a pretty strong mus- 

 cular layer (mostly annular fibres), and internally a coating of 

 regular, hexagonal epithelial cells, with small dark aggregations 

 of granules (certainly oil-drops) in the middle, often detaching 

 themselves in greater quantity behind the eggs, and, as horny 

 structures, probably contributing to the formation of the chitine 

 membrane of the chorion. It widens pretty rapidly at its com- 

 mencement, that is to say, where the tuba passes into it. An- 

 teriorly the uterus narrows rather quickly, and when it is double 

 or multiple, the branches unite at an acute angle quite in front, 

 towards the vagina. The function of the uterus, in which the 

 eggs acquire their round form, is certainly in part the enveloping 

 of the eggs with the chorion, and in part to allow them to pass 

 through that well-known remarkable process of segmentation, 

 which we shall mention particularly at the conclusion. 



As regards the coating of the eggs with the chorion, this takes 

 place in the following manner. A solidifying mass, secreted from 

 the side walls of the uterus, is deposited in concentric and con- 

 stantly increasing layers round the vitelline membrane, which 

 often adheres to them in little folds as the innermost layer. By 

 this means the egg-shell constantly becomes thicker and more 

 resisteut. This outer egg-membrane or chorion is usually smooth, 

 rarely tubercular, thick, less transparent, and always round and 

 without appendages, as in the human Nematoida. In particular 

 species, however, the chorion only remains for a short time in its 

 simple form, and acquires a sort of process of very various form, 

 sometimes at the anterior end, sometimes at the posterior one, 

 and sometimes at both. Of the human Nematoida, only two 

 deserve especial mention on account of this chorion. The eggs 

 of the Trichocephali, like those of the Trichosoma, are distin- 

 guished by a short diverticulum, as it is called, which is certainly 

 produced by the deposition of the secretion producing the chorion 

 only upon the sides, and not upon the ends, probably in conse- 

 quence of a structure still undiscovered, and of peculiar move- 



