294 ANIMAL PARASITES. 



ing to Leuckart, in a certain number of other animals. The 

 clear, non-granular boundary line of the yelks of young eggs 

 may easily be taken for a membrane, whilst the true vitelline 

 membrane is only produced subsequently according to Thompson, 

 probably by the condensation of the limiting zone. Neither 

 Nelson, Bischoff, nor Thompson, believe in the existence of a 

 micropyle on the spot where the eggs, according to Meissner, 

 have separated from their stem. 



Meissner, indeed, describes this process otherwise, and con- 

 siders the vitelline substance to be deposited within the ready 

 formed vitelline membrane. He describes this as follows : — In 

 the vitelligene the central mother-cell first becomes filled with a 

 granular mass (vitelline granules). When the mother-cell is 

 quite full, the vitelline granules pass through the open peduncles 

 or through the apices of the above-mentioned triangles, into the 

 interior of these triangular bodies (daughter-cells, daughter-eggs), 

 the delicate walls of which become the vitelline membrane. The 

 mother-cells or mother-eggs, as the centres of the stellate discs, fall, 

 at the same time, into a common axis, which, however, is no true 

 axis, but an axial line (rhachis), which really only occurs in the 

 Strongyli. The daughter-eggs are arranged in a radiate form 

 round and upon this axis. The eggs are seated, like currants, 

 singly upon a longer or shorter stalk, which passes directly into the 

 vitelline membrane of the mother-cell. Towards the germstock 

 the rhachis and eggs gradually become smaller and more delicate: 

 but towards the albuminigenous tube thicker, larger, and more 

 mature. In the albuminigenous tube this arrangement of the 

 eggs, and with it the rhachis, ceases. The young eggs may con- 

 sequently be regarded as diverticula of the rhachis itself, on the 

 walls of which the individual, ready-formed germ-cells, therefore, 

 probably attach themselves, and become gradually surrounded by 

 it. If the rhachis could be traced into the germstock, we 

 should have to regard it as the germigene itself; but as it only 

 occurs within the vitelligene, and a distinct germigene exists in the 

 Strongyli, we must now give up the idea that this actually existing 

 rhachis is the germigene, however plausible this supposition might 

 be. Individual ova, on separating, pass in a triangular form into 

 the albuminogene. 



3. The albuminogene (Ehveissschlauch).— -It begins with a con- 

 siderable dilatation where the vitelligene is narrowed by a 

 sphincter formed by a small layer of annular muscular fibres, and 



