ORIGIN OF THE CILIATED MANTLE. 



723 



early stage, into two concentric lamellse, between which lie a 

 number of coarse-grained protoplasmic masses, with numerous, some- 

 what large nuclei, which owe their origin to the multiplication of the 

 few originally present. Thus the ciliated mantle does not consist, 

 as formerly supposed, of a simple membrane, but of a double one, 

 as has since been independently discovered by Schauinsland and my- 

 self. Even at a very early stage may be detected short and delicate 

 ciliated hairs on the external membrane, but these do not become 

 very distinctly visible till after some time, when they have considerably 

 increased in size. 



But while the mantle has originated in the manner which we have 

 thus shortly described, the nucleated mass of embryonal cells in its 

 interior has been transformed by continuous en- 

 largement and cell division into a clear solid body 

 of round form, which is somewhat sharply defined, 

 and which may be recognised as the true embryo 

 by the rapid increase of the primary cilia. 

 And this is stUl more evident from the fact that 

 in the meantime the yolk-cells surrounding the 

 mantle have, for the most part, entirely broken up, 

 and, except numerous granules, have only left 

 some larger or smaller irregular drops. One may 

 occasionally still recognise some altered yolk-cells, with fluid contents, 

 and with few granules. 



When the development has progressed further, the previously 

 visible motions of the embryo become more marked. The body 



V_^^ 



Fig. 385.— Embryo 

 oiBotArioeephalus Tatus 

 in the egg. 



Ilfi')'!'!//'/.' 





v;iffl}% 



Tig. 386.— Free ciliated embryos of Bothriocephalus laius. ( x 500.) 



shortens and lengthens alternately, and the hooks are moved, until 

 ■the lid opens and aff£^d|^an^ gxi^ Jn^sli^-g out, the body and its 



