254 ANIMAL PARASITES. 



of the animal passes over into the central one, a straight branch 

 runs horizontally towards the median line of the animal, and 

 unites with the branch of the opposite side. Rarely (about once 

 in fifty examples), instead of one main stem coming from the 

 side, we meet with two which unite at an acute angle, but 

 always before the middle line, to form a single branch, which 

 then runs horizontally towards the branch of the other side, 

 and behaves just as we have above described. The point 

 of union of these two stems is the only anastomosis which the 

 two vitelligenes form throughout. By this union a cordate dila- 

 tation is produced at this spot, from which a very narrow canal 

 issues anteriorly in fine, scarcely visible convolutions. Soon after- 

 wards this canal becomes somewhat wider, and we meet with 

 separate pale eggs, surrounded by true egg-shells, which are pro- 

 bably produced by the conjunction of the structures of the vitelli- 

 gene, and those furnished by the organ mentioned under a, after 

 the ducts of the two organs have united. The contents of these 

 yelk-sacs are yelk-corpuscles, yelk-globules or vitelline cells, 

 which during their passage through the efferent duct above 

 described acquire all sorts of forms, fitting themselves to the 

 passages through which they must pass. Each of these vitelline 

 agglomerations consists of single yelk-globules, measuring 

 about 0-0018 mill. = 0008"' Par. or Vienna. In the cordate 

 dilatation the agglomerations have about the following size : 

 0028 mill. = 0012'" in length, and 0-014 mill. = 0006'" in 

 breadth, and they consist of from 30 — 50 individual yelk- 

 globules. When quite fresh the yelk-sacs appear white or pale 

 yellow, but when the animals are allowed to lie for a good while in 

 bile, they acquire a darker-yellow colour. They lie in the midst 

 of the parenchyma of the body, but nearer to the ventral than 

 the dorsal surface. 



c. The oviduct, which follows these, is very short, forms some 

 very wide spiral turns, and passes without any perceptible 

 boundary into the uterus ; indeed it might, perhaps, be deno- 

 minated a uterus even from its commencement. 



d. The true uterus is turned more towards the ventral surface 

 of the animal. At first, the dimensions of the convoluted simple 

 uterus are small, the eggs lie in a single layer, and still possess 

 white, or rather colourless shells, through which shine their con- 

 tents, similar to those of an egg in process of segmentation ; 

 subsequently, the convolutions gradually become wider, and the 



