722 OCCUEKENCE 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. 3S2. — Ovum of Boihriocephalus 

 latus, after Sohauinsland, with four 

 embryonic cells and enveloping cells 

 on the granular yolk ( x 600). 



Fig. 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 m 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 Taenia 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 Boihriocephali 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 

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

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

 Digitized by Microsoft® 



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. 

 (After Sohauinsland.) 



