722 OCCURRENCE AND DEVELOPMENT OF BOTHRIOCEPHALUS LATUS. 



" cellules albuminogenes." But the four embryonic cells lying inside 

 the yolk are not all of the same nature. There is one among them 

 which is seated as a cap upon the others, and which pursues a separate 



FIG. 382. Ovum of Bothriocephalus 

 latus, after Schauinsland, with four 

 embryonic cells and enveloping cells 

 on the granular yolk ( x 600). 



Fio. 383. Another ovum, with 

 covering cells apposed to the em- 

 bryonic body. ( x 600. ) 



course, inasmuch as, instead of dividing further along with the others 

 and helping to form the embryo, it grows round them, and, along with 

 its descendants, is gradually modified in the 

 course of time into the ciliated mantle. As van 

 Beneden has observed and I can now confirm 

 the statement the chitinous shell surrounding 

 the embryo of Tcenia originates in exactly the 

 same way. It is the result not of a simple 

 secretion, but of a number of cells (" cellules 

 chitinogenes "), which at an early stage 

 separate from the rest and grow round them 

 in the form of a pellucid membrane, which 

 gradually thickens, and is modified into 

 the subsequent shell. The ciliated membrane 

 of the Bothriocephali is thus morphologically 

 equivalent to the firm egg-shell of the cystic 

 tape- worms and the associated egg-membrane, 

 but not, as I formerly (p. 326) believed, to the 

 peripheral border cells. There is, indeed, 

 both anatomically and physiologically, a con- 

 siderable difference between the two organs. 

 From the originally thin and transparent 

 envelope there arises no thick and firm 



FIG. 384. Egg of Both- 

 riocephalus, with imperfectly 

 developed embryo, being ex- 

 pelled by compression. In 

 the interior of the egg-shell 

 are seen the remains of the 

 yolk-cells, and the enveloping 

 membrane with its nuclei. 

 (AfterSohauinsland.) 



chitinous shell, but a soft membrane, which, by the separation of 

 the primarily closely apposed cell- walls, is divided, at a somewhat 



