552 



The Animal Kingdom 



agus and five radial canals. The madreporite, however, is internal. From 

 the ring canal extend several large Polian vesicles which may produce 

 amoebocytes. The fluid in many of the sea cucumbers is reddish in 

 color due to the presence of hemoglobin-containing cells. 



INTESTINE 



RESPIRATORV. 

 TREE 



LONGITUOINAL 

 MUSCLES 



CLOACA 



Fig. 182. — The anatomy of a holothurian, Thy one briar eus. (From Coe: Echino- 

 derms of Connecticut, Connecticut Geological and Natural History Survey.) 



The sexes are separate and the gonads are bushy structures within 

 the coelom. They open to the outside through a small opening within 

 or near the ring of oral tentacles. Fertilization, as usual in the mem- 

 bers of this phylum, is external and development is through a larval 

 form known as an auricidaria (Fig. 181, C). Some of the species brood 

 the young in special pouches on the body surface. The sea cucumbers 



