THE DEVELOPMENT OF THE EMBRYO. 325 



albuminous mass, which takes the place of the yolk, by a structure 

 which in certain Tseniadse also gradually assumes a firm consis- 

 tence. Kegarding the structure of the horn-shaped or thread-like 

 appendages, we have only a single observation of E. van Beneden's 

 to go upon, according to which they are protruded subsequently 

 during the division of the yolk. The statement rests upon the exami- 

 nation of Tcenia bacillaris, which, however, differs in so far that the 

 horns are drawn back during the growth of the embryo, and leave no 

 trace of their presence in the mature eggs. In other cases even the 

 newly formed egg is provided with these appendages. So it is at 

 least in the larger Cystotcenice ; but the appendages vary greatly in 

 individual cases, both as to number and mode of occurrence. 1 I find 

 them most constantly in Tcenia saginata and T. marginata (in the latter 

 oftener one than two), but comparatively seldom in T. serrata. They 

 can also be sometimes demonstrated in the younger eggs of T. elliptica, 

 where again they usually occur singly. I think that they probably 

 originate when the transference into the uterus takes place, and in a 

 purely mechanical manner, by drawing out into threads the secretion 

 supplied by the shell-gland. 



As has long been observed in the case of T. elliptica, certain other 

 alterations take place in the eggs of Tcenice, after the complete maturity 

 of the embryos, for they are collected in groups and surrounded by a 

 firm common envelope (p. 317). The groups always correspond to the 

 contents of a uterine branch, from the walls of which the enveloping mass 

 is distinguished as an originally clear granular substance. The same 

 may be observed in T. litter ata, except that in this case the simply 

 tubular uterus envelops all its egg-masses within a single capsule. 



What we have hitherto said regarding the embryonic development 

 of the Tseniadae is based primarily and specially on observations made 

 by van Beneden and Moniez in certain smaller species. In the species 

 of Cystotcenice which I have specially investigated with regard to these 

 processes, the state of matters is somewhat different, although gene- 

 rally similar, so that it looks as though there might be many modifi- 

 cations in this respect, with which we are as yet only slightly 

 acquainted. 2 



The first phases of the development, before the fourfold division 

 of the eggs, exhibit, it is true, no peculiarities. The yolk-balls are 

 pale cells of about 0'013 mm. with a large vesicular nucleus. They 



1 I owe my first acquaintance with these structures to a communication from my 

 honoured friend E. van Beneden, who discovered them in the eggs of Tcenia saginata. 



2 [E. van Beneden has recently made this process the subject of a thorough investiga- 

 tion, " Recherches sur la developpement embryonaire de quelques Tdnias," Archiv. d. Biol., 

 t. ii., pp. 183-210, 1881. R. L.] 



