PLATHELMINTHES 193 



The formation of the larval membranes in the Trematodes and Ces- 

 todes recalls in a striking manner the Amnion and Pilidium in the Nemer- 

 teans. Since, however, similar processes do not occur in the Turbellaria, 

 — to which relationships are shown by the Trematodes and Cestodes on 

 one side, and by the Nemerteans on the other, — and since the Turbellaria 

 are to be considered as the more primitive forms, we have here to do with 

 only analogous phenomena. 



The embryonic development of the Taeniadae differs 

 to some extent from that of the Bot]irioce2)halidoe, but leads 

 finally to a similar result (Leuckart, No. 8 ; Moniez, No. 9 ; 

 E. VAN Beneden, No. 2). A difference is caused from the 

 very beginning by the yolk-material bestowed upon the egg 

 being less abundant, or not in the form of distinct cells. In 

 Tcenia serrata the egg- cell lies embedded in this yolk-material. 

 In other cases the yolk appears to enter into still more inti- 

 mate relations with the egg-cell ; however, it appears from 

 the somewhat various statements of the authors concernino^ 

 the different forms that even in these cases the nutritive 

 material becomes separated as early as the first divisions of 

 the egg. There are one or several rather voluminous, gene- 

 rally granular cells, which are thus at first constricted oft* and 

 then consumed, while the other cellular matter multiplies 

 further. In Tcenia cucumerina, it is true, the entire egg is 

 said to be transformed directly by means of a rather regular 

 cleavage into the embryonic cell-mass (Moniez). In the 

 further development of the Taeniadae we can find again the 

 characters which we observed in the Bothriocephalidae, al- 

 though the details of the process are somewhat different. 

 In the Taeniadae also certain cells detach themselves at an 

 early period, and grow around the germ as its enveloping 

 membrane. In the Taeniadee known as the Bladder-tape- 

 worms, the second membrane may present an appearance 

 somewhat different from that with which we have thus far 

 acquainted ourselves. It becomes cuticalarized, assumes a 

 radially striated appearance, and thus finally forms a firm 

 membrane about the embryo, which even in this stage is 



todesthe subcuticular matrix is independent of tbe connective-tissue body 

 parenchyma, and explains how in the embryo an ectodermal cell-layer 

 still remains behind after the casting off of the ciliated mantle.— K.] 

 K. H. E. () 



