258 ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



which Pt. ruficollis seems to be more closely allied than with any other species, 

 the genital region is less than half the length of the branchial region (Hill). 



The hepatic region occupies approximately the third quarter of the body reckoned 

 from the front. The rich brown colour which characterises this region is concentrated 

 along parallel lines which run diagonally in two directions, decussating and so pro- 

 ducing a striking lattice-work pattern. This condition could also be expressed by 

 saying that the dermal annulations are broken up into diamond-shaped islets. 



In the branchial region the dorsal vascular trunk is distinct and coloured red ; 

 otherwise the dorsal vessel is inconspicuous from outside. The ventral vessel on the 

 contrary is very conspicuous with its deep red colour; it is bounded ou each side 

 by a longitudinal clear neutral-tinted area. 



The general shape of the body is subcylindrical with a diameter of about 4 mm. 



PROBOSCIS. 



The layer of circular muscles which lies next below the basement-membrane of 



the epidermis is thin, as is usual in Ptychodera, while the longitudinal muscles of 



the proboscis are arranged in radial bundles. The central cavity of the proboscis is 

 not surrounded by a feltwork of conjunctive fibres. 



Central Complex. 



The anterior or distal extremity of the central complex of the proboscis in 

 Pt. ruficollis differs greatly from the condition met with in the two species described 

 above. The stomochord is not attenuated in front but terminates bluntly; the lumen 

 extends practically to its distal end, and there is thus no solid prolongation. 



The pericardium is bifid anteriorly, being produced forwards into two blind 

 pouches, each of which is accompanied by the corresponding half of the glomerulus, 

 for a short distance beyond the anterior limit of the stomochord (PL XXX. Fig. 24). 

 This condition is comparable to what takes place in the Spengelidae, where, as was 

 first described by Spengel in Schizocardium and Glandiceps, the pericardium is produced 

 anteriorly into a pair of pericardial auricles (Herzohren). 



The cavity of the pericardium is quite filled up by loose spongy tissue over a 

 short stretch at its posterior end. 



The ventral septum of the proboscis extends almost to the anterior extremity of 

 the stomochord, its anterior free edge passing very obliquely downwards and backwards. 

 It will be remembered that in Pt. flava the ventral septum ceases shortly in front 

 of the dilated region of the stomochord, remote from the anterior end of the central 

 complex. 



At the front part of the coecal dilatation of the stomochord the lateral portions 

 of the ventral coecum are seen to be projected forwards as paired lateral pouches 

 (PI. XXX. Fig. 25). It is clear that in many species of Enteropneusta the lateral 

 pouches have to be considered equally with what Spengel has described as the ventral 

 coecum only. In Pt. australiensis. Hill (loc. cit.) describes and figures the lateral 



