98 



ZOOLOGY. 



layer of cells, nor of any organs, all the animal and vegeta- 

 tive functions being accomplished by the activity of the 

 ectodermic cells and of the single axial cell. There is no 

 mesodermic cell or cells. On account of these characteris- 

 tics. Van Beneden 

 regards these or- 

 ganisms as forming 

 the type of a new 

 branch of the ani- 

 m a 1 kingdom, 

 which he distin- 

 guishes as Mesozoa. 

 He places the 



I 



r~\ 

 'Q\ 



branch or sub- 



kingdom, between 

 the Protozoa and 

 all the many-celled 

 animals (Metazoa), 

 and includes the 

 hypothetical Gas- 

 trceades of Haeckel 

 in the branch. 

 While this position 

 may prove to be 

 the correct one, we 

 should prefer, while 

 not overlooking the 

 resemblance of the 

 Dicycmiclce- to the 

 Infusoria, and even 



Fig. 62. a, DicyernellaWagneri ; g, g. germigenes ; n, 

 nucleus of the axial cell ; b, the spherical germ of Dicye- the GrTeffarinSB to 

 inella, with its striated nucleus ; c, the same beginning 

 to undergo self-division ; d, final stages of self-division 

 imorula) ; e and f, infusoriform embryo; h, germs of 

 the vermiform embryos of Dicyema typus ; i, gastrula 

 of the same ; k, I, m, o, different stages of vermiform 

 larvae of Dicyema typus, all highly magnified. After E. 

 Van Benedeu. 



wait for more light 



on the development 

 of the parasitic 

 P 1 a t y h e 1 m i n t h 

 worms. It is not improbable, on the one hand, that the 

 DicyemidcB, retaining their parasitic life, are retrograde 

 forms, which have originated from some low Cestoid or 

 Trematode worm, and bear the same relation to them, the 



