PHYLUM ECHINODERMATA 



395 



flattened nucleated corpuscles containing a red colouring matter 

 hemoglobin almost identical with that which gives the red 

 colour to the blood of the higher animals. 



gen. op 



=^ gen du, 



mad. can 

 int ves 



Long frucs - 



to ng rrut 



FIG. 334. Internal organs of a Holothurian as een when the body-wall is divided along 

 the middle of the, dorsal surface. 6. w. body-wall ; circ. WM. circular layer of muscle ; 

 cl. cloaca ; cl. op. bloacal opening ; cuv. org. (Juvieran organs ; gen. op. genital aperture ; 

 gen. du. genital duct ; gen. gl. gonad ; int. intestine ; inter, oss. inter-ambulacral ossicles ; 

 int. ves. intestinal haemal strands ; long. mus. longitudinal band of muscle ; mad. can. 

 madreporic canal ; mes. mesentery ; pol. ves. Polian vesicle ; rad. amb. radial ambulacral 

 vessel ; rad. oss. ambulacral ossicles : ri. bl. ves. ring strand of haemal system ; resp. 

 respiratory trees ; ring-ves. ring-vessel of the ambulacral system ; stom. stomach. (After 

 Leuckart.) 



The enteric canal is, as already mentioned, surrounded at its 

 oral extremity by the circlet of tentacles, and within these, when 

 they are fully exserted, is a narrow peristome with the mouth in 



