140 



ZOOLOG Y. 



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 Beueden 

 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 

 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 



Fig. 93. a, DicyemellaWagnen ; ff, g. germigenem ; , 



icleus of the axial cell ; b, the spherical germ of Dicye- the (jrregarinaS, to 



wait for more light 

 on the development 

 of the parasitic 

 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 

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



nucleus of _,____. 



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

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

 (morala) ; e and f, infusoriform embryo; A, germs of 

 the vermiform embryos of Diiyema typus ; i, gastrula 

 of the same ; k, I, m, 0, different stages of vermiform 

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

 Van Beneden. 



