OUK KNOWLEDGE OF NEW ZEALAND HOLOTHURIANS. 105 



Anteriorly, each is produced into a process which is deeply cleft at its extremity; 

 posteriorly, each is produced into two long and slender processes ending at the 

 level of the circular canal. These two processes are closely approximated at 

 their posterior ends, hut in front the space between them widens out into a 

 cleft which continues almost to the anterior end of the plate. The entire 

 radial plate is formed by a number of roughly rectangular pieces, which form 

 a single row down each process and are fairly regularly arranged. The inter- 

 radial plates are somewhat shorter and a little wider than the radials. Each 

 is concave behind and anteriorly produced into a pointed tongue-like process. 

 Each inter-radial plate is composed of a number of small polygonal pieces. 



The pharynx leads into a very thick-walled narrow oesophagus (fig. 15, oe.) 

 a little more than 1 cm. long. After a slight constriction this widens out into 

 a thin-walled intestine (i.) which exhibits the usual S-like curvature. The 

 first descending limb is much convoluted, the ascending limb rather less 

 so, and the last descending limb is straight. The first two limbs are kept in 

 position by the dorsal mesentery and the last part by the right mesentery. 



The terminal part of the alimentary canal is dilated into a cloaca in the 

 dorsal wall of which open the two large respiratory trees. The cloaca is kept 

 in position by a large number of muscle-fibres, radially arranged, running 

 from its outer surface to the body-wall. 



The respiratory trees (fig. 15, r.t.) are richly branched and extend almost to 

 the anterior extremity of the body-cavity, the left tree being slightly larger 

 than the right. They unite immediately before opening into the cloaca. 



The five longitudinal muscle-bands are well developed. Although single 

 whilst on the body-wall, at the anterior end each becomes double as soon as 

 it passes on to the introvert, and runs along the latter as tv,"o very thin strips 

 of muscle. Each strip is attached to the corresponding half of the bifurcate 

 process of one of the radial plates. 



The five retractor muscles of the pharynx are very stout bands attached to 

 the radials at one end and to the corresponding longitudinal muscle-bands at 

 the other. Their points of attachment to the radials are remarkably small, 

 considering the thickness of the muscle, and in the specimen before us have 

 all become detached from the corresponding plates. 



Arising from the ambulacra! ring, by a wide base, is a long thin Polian 

 vesicle extending, in the retracted specimen, almost to the posterior end of 

 the body-cavity (fig. 15, p.). The madreporic canal (fig. 15, m.} is a slender 

 sinuous tube which ends in a small madreporite, situated on the dorsal 

 mesentery. 



Running along the intestine are the usual dorsal and ventral vessels. 



The gonads (fig. 15, g.) consist of two bundles of slender radiating caeca 

 placed right and left of the dorsal mesentery at about one-third the length of 

 the animal from the anterior end (in the retracted state). As they appear to 

 contain nothing but ova, this species is probably dioecious. A very slender 



