284 



ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



pits. In fact, in section, it appears as a replica of the dorsal submedian tract. 

 Below it the layers of longitudinal muscles is thinner than in the neighbouring 

 tracts and posteriorly this layer thins out almost entirely at this place (PI. XXXII. 

 Fig. 58). Opposite to the glandless epidermal tract a tract of thickened columnar 

 intestinal epithelium may be observed at the region of the hepato-abdominal transition. 



Throughout the entire length of the hepatic region there is a pair of large 

 lateral splanchnic vessels lying against the wall of the gut at the outer base of 

 the internal hepatic saccules and at a corresponding level in the anterior abdominal 

 region (PI. XXXII. Fig. 58). They occupy the position in which a large vessel is often 

 to be seen in Ptychodera flava (and doubtless in others) at the base of the lateral 

 septum (cf. PI. XXIX. Fig. 13). In the Spengelidae there is no lateral septum. A 

 similar pair of vessels has been described by Spengel in Sch. brasiliense, Gl. hacksi 

 and Bal. kowalevskii (Spengel, Monograph, p. 575). 



Caudal Region. 



The caudal region of S. alba has no very striking characteristics. The longitu- 

 dinal muscles become feeble and the circular muscles do not suffer any change, there 

 being no special sphincter round the anal opening. There is no band-like or keel- 

 shaped pygochoi'd, but the median ventral epithelial tract of the hind-gut consists 

 of enlarged columnar cells with clear vacuolar contents ; it is therefore no doubt to 

 be regarded as a pygochord which has retained its epithelial position in the wall of 

 the gut (PI. XXXII. Fig. 60). 



OECOLOGY. 



The complete unique male specimen which I obtained of this specimen was taken 

 by me from a submerged hillock of sand (resembling a truncated mole-hill) at low 

 water off Vulcan Island (Rakaiya) Blanche Bay, New Britain. It broke itself into 

 three pieces but nothing was lost. The species appeared to resemble Sp. porosa in 

 its mode of life. It is not a burrowing species like Pt. carnosa, but lives in the 

 superficial loose layers of (volcanic) sand like Sp. porosa and Pt. flava. 



On account of the length of the proboscis one might suppose, from its external 

 characters, that it was a Balanoglossus s. str. It was quite alone although Pt. carnosa 

 occurs in the same locality. 



