18 



THE SUB-KINGDOM CCELENTERATA. 



by means of a wide inferior aperture (Jig, 2, f 



and g). 



Some Actinozoa exhibit a further sub-division 



of each of the two primary blastodermal layers 

 into other secondary membranes, foreshadowing a 

 structure so constantly met with among the higher 

 animals, just in the same manner as, in a few of 

 the more advanced stomatode Protozoa, an in- 

 distinct differentiation of the body into layers 

 indicates a condition which is manifested, without 

 exception, by the immature forms of the four re- 

 maining sub-kingdoms. 



Development of Animals. 











The organism does not ex- 

 hibit true layers. 



Protozoa. 



A blastoderm is formed, 

 which divides into inner and 



outer layers. 



The alimentary canal freely 

 communicates with the somatic 

 cavity. There is no distinction 

 between neural and haemal 

 regions. 



CCELENTERATA. 



The two layers of the blas- 

 toderm become further diffe- 

 rentiated.. The alimentary 

 canal has no direct communi- 

 cation with the somatic cavity. 

 Distinct neural and haemal 

 regions appear. 





The haemal region is first 

 developed. The mouth opens 

 on the neural aspect. There 

 is no segmentation of the blas- 



toderm. 



Mollusca. 



The neural region is first 

 developed. The blastoderm 

 may divide into segments. 



The mouth opens on the 

 neural aspect, towards which the 

 limbs are turned. 



Annulosa. 



The mouth opens on the 

 haemal aspect, towards which 

 the limbs are turned. A pf 1- 

 mitive groove, dorsal and vis- 

 ceral plates, are formed. 



Vertebkata. 







