84 



INVEETEBEATA 



CHAP. 



formed later by the fusion of the two layers of the body wall at the 

 oral pole aiid their perforation at this point. 



The larva possesses an anterior wisp of long cilia, the cells carry- 

 ing which are excessively attenuated and have all the appearance of 

 sense cells; and at their bases are a few rounded cells with tails, 

 obviously ganglion cells. In the larvae of Agaricia according to 









end 



Fig. 63 — Stages in the development of the larva of Actinia 



equina. (After Appellof.) 



A, stage just before the formation of the mouth, the endoderm is already absorbed over the spot where 

 the mouth will be formed. B, stage when the mouth is formed. 0, stage after formation of stomodaeum. 

 D, aboral pole of free-swimming larva much enlarged, dl, long aboral cilia ; n.f, nerve fibres. Other 

 letters as before. 



Duerden (1902), although there is no bunch of long cilia at the aboral 

 pole, there is at this spot a comparatively thick layer of nerve fibres 

 (Fig 62). 



In the species Actinia hermudensis, the development of which 

 has been worked out by Gary (1910), although the egg passes through 

 the earlier stages of development within the coelenteron of the 

 mother, yet the endoderm appears to be formed by invagination 



