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- 

 mal kingdom, 

 which he distin- 

 guishes as Mesozoa. 

 He places the 

 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 

 DicyemidcB to the 

 Infusoria, and even 

 the Gregarinee,. to 



wait for more light 



Pig. 62. a, Dicyemella Wagneri ; g, g. germigenes ; n, 

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

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

 " ilf-flvision 



to undergo self -division ; d, final etages'orself- 



(monila) ; e and /, infusoriform embryo ; A, germs of , -i -i i 



the vermiform embryos of Dicyema typus ; ifgastrula On the development 



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



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



, , 

 OI tne pai'aSltlG 



Platyhelminth 

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

 Dicyemidce, 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 



