THE SUB-KINGDOM C(ELE^^TEKATA. 



by means of a wide inferior aperture {fig, 2, / 

 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 w4iich is manifested, without 

 exception, by the immature forms of the four re- 

 maining sub-kingdoms. 



Development of Animats. 



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. 



CCFXEXTERATA. 



\ 



• The hffimal region is first 

 developed. The mouth opens 

 on the neural aspect. There 

 is no segmentation of the blas- 

 toderm. 



MoLLrSCA. 



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 ha:ual 

 regions appear. 



I 



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. 



AXNX^LOSA. 



The mouth opens on the \ 

 hpemal aspect, towards which 

 the limbs are turned. A pri- 

 mitive groove, dorsal and vis- 

 ceral plates, are formed. 



Veu'iebrata. 



