256 



ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



Nevertheless, one is present. As shown in PI. XXIX. Fig. 16, it is a very high, thin 

 band with slightly dilated distal edge abutting upon the ventral vessel. It consists of 

 ordinary cells as in Pt. flava. It probably does not possess great staying power in 

 the present species. A pygochord seems to be of very general occurrence among the 

 Ptychoderidae and affords a useful specific character. 



OECOLOGY. 



Pt. carnosa burrows deeply in the sand and can draw itself along wdth astonishing 

 rapidity. Its presence is betrayed by massive castings, which sometimes occur in such 

 numbers as to form an important feature in the landscape at low tide. It lives at 

 a depth of from one to two feet in the sand, both volcanic and coral, and may be 

 taken anywhere between Cape Gazelle and the island of Matupi in Blanche Bay, New 

 Britain. I first found it in Matupi. 



In the same burrows another smaller species is to be found, namely, Pt. ruficollis n. sp. 



It breaks up into longer or shorter lengths upon slight provocation. I do not 

 know whether or not fragments of the trunk would regenerate a head. There can 

 be no doubt however as to the ability of the animal to regenerate its proboscis, 

 which is often found more or less injured. 



Often in the process of defaecation the caudal end of the body is thrown off 

 with the castings. An isolated piece, two or three inches long, of the abdominal 

 region will always turn itself inside out. 



The enormous size of the collar in this species, in some individuals more than 

 in others, suggests that it not only assists the proboscis in the acts of burrowing and 

 progression but even tends to supersede the proboscis. In other words, the collar of 

 this species, and probably of some others, is more important than the proboscis 

 as an essential organ of progression. This is therefore an indication of modification of 

 function of the proboscis, and all such indications, however slight, should be carefully 

 recorded. 



