NOTES ON EMBRYOLOGY AND CLASSIFICATION. 441 



Tabular Vieio of the Phyla of the Animal Kingdom. 



ANIMALIA. 



Organisms incapable of assimilating either N or C from their simpler 

 water-soluble compounds, and therefore provided (excepting parasites) with 

 the means of ingesting and acting upon the solid substance of other 

 organisms. 



Grade I.— PLASTIDOZOA. 



Animals consisting of single plastids, or of groups of plastids not dififer- 

 entiated into cell-layers. 



Peotozoa. 



Grade II.— ENTEROZOA. 



Animals consisting of many plastids primarily arranged in two layers 

 surrounding a food-receiving cavity — the enteron (the lumen of which is 

 obliterated in some parasites). 



Grade 1 (of the Enterozoa) CCELENTERA (Diploblastica). 

 Enterozoa in which the enteron "remains as a continuous cavity, either 

 simple or much ramified, coextensive with the body wall. Persons telosto- 

 miate, generally with radial symmetry. 



Thylim 1. — Porifera. 

 „ 2. — Nematophoka. 



Grade 2 (of the Enterozoa) CCELOMATA (Triploblastica). 



Enterozoa in which a second cavity containing hsemolymph — viz. the 

 coelom — entirely shut off from, though in its origin a part of, the enteron, 

 is developed between the body wall and tlie enteric wall. Persons prima- 

 rily prostomiate, bilaterally symmetrical, with paired nephridia and nerve 

 tracts. 



Fhl/lum 1. — ECHINODEBMA. 



Branch a. Ambulacrata. 

 „ b. Tentaculata. 

 Phyl PhyL Thyl. 



2. — Platyelmia. 4. — Gephyr^a. 6. — Enteropnetjsta. 



Br. a. CiJiata. I | 



„ h. Suctoria. 1 j 



3. — Appendiculata 5. — Mollusca (Meso- 7. — Vertebkata. 



(Parapoda). poda), Br. «. Urochorda. 



Br. a. Chsetopoda. Br. a. Eucephala. „ b. Cephalo- 



„ h. Botifera. „ b. Lipoce- chorda. 



„ c. Gnatho- phala. „ c. Craniata. 



poda. 

 Pliyl. 8. — Nematoidea. Fhyl. 9. — Ch^toonatha. 



N.B. — On account of their very dubious aflBnities and probable degenera- 

 tion, no attempt is made in the above synopsis to include the following 

 forms : the Gastrotricha (Chaetonotus, &c.), Desmoscolex, Echinoderes 

 and the parasites Dicyemida and Echinorhynchus. 



