— 19 - 



f with nematocysts ; symmetry radial, or at least funda- 

 mentally so ; mostly colonial, or fixed, or both ; if fixed, 

 with an excreted calcareous or organic skeleton : diœcious, 

 or very rarely hermaphroditic ; asexual reproduction 

 by budding and fission occurs in all the included groups 



Cœlenterata. 



no nematocysts (except in a single genus) ; with eight 

 rows of vibratile plates formed of fused cilia : symmetry 

 bilateral ; solitary, and almost invariably pelagic ; herma- 

 phroditic and without asexual reproduction Ctenophora. 

 primary axis of the gastrula not becoming the axis of the 

 adult, which is always elongated with a head end and more 

 or less perfectly quadrilateral ; with a centralized nervous 

 system and an excretory system 



no vascular nor respiratory systems ; no true cœlome 

 f mouth in the center of an elaborate food collecting 

 apparatus ; a gastric mill or muscular gizzard may 

 be present 



g' with a ciliated trochal disc and a straight or nearly 

 straight digestive tube with a dorsal posterior anus ; 

 free living and not forming colonies ; but partheno- 

 genesis occurs Rotifera. 



with ciliated tentacles forming a lophopore about the 

 mouth, and a U-shaped digestive tube ; fixed or colonial, 

 usually both 



anus close to the mouth within the lophophore ; 

 tentacular crown not introversible, but the tentacles 

 capable of being flexed and partially rolled up ; 

 no body cavity ; a pair of small nephridia present 



Calyssozoa. 



anus not included within the area of the lophophore ; 

 anterior portion of the body retractile ; tentacles not 

 capable of being flexed or coiled ; a spacious body 



cavity present ; no nephridia Polyzoa. 



P no ciliated food collecting apparatus ; mouth absent, 

 or circular or triangular 



g' no body cavity ; body more or less flattened dorso- 

 ventrally 



h' with a mouth and gastric cavity, the latter forked 

 or ramified 



i' free living, with a ciliated ectoderm containing 

 rhabdites and sometimes nematocysts ; organs for 

 attachment exceptional ; mouth on the anterior, 

 middle or posterior portion of the ventral surface 



Turbellaria. 



parasitic, the ectoderm not ciliated and without 

 rhabdites or nematocysts ; organs for attachment 

 (suckers or hooks) always present ; mouth anterior 



Trematoda. 



no mouth or alimentary canal ; head (scolex) radially 

 or bilaterally symmetrical ; body more or less perfectly 

 bilaterally symmetrical ; usually imperfectly colonial 

 by continuous budding (modified strobilization) 



Cestoda. 



g' with a more or less developed body cavity ; body 

 rounded in cross section 



(400) 



