270 



ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



Central Complex. 



The pericardium is bifurcated in front and the right and left halves of the 

 glomerulus are likewise produced for a short distance in front of the body of the 

 stomochord, but the pericardial auricles (Herzohren) are not long, definite structures 

 as described by Spengel in Schizocardium but moderately developed (PL XXXI. Fig. 37). 

 Of the two anterior horns into which the glomerulus is produced the left is larger 

 and longer than the right in my preparations, and in correspondence with this con- 

 dition the right pericardial auricle is feebly developed, the bulk of the pericardium and 

 central blood-space passing over to the left division of the glomerulus. The left auricle 

 can be traced through about half the course of the left horn of the glomerulus. 



The ventral septum of the proboscis commences at the junction of the vermiform 

 process with the body of the stomochord. The latter is somewhat flattened transversely 

 in front and contains a multiple, interrupted lumen. In addition to the usual elongated 

 fibre-like interlacing cellular tissue, there are numerous deeply staining gland-cells in 

 the neighbourhood of the lumen. At some points the lumen is reduced to the merest 

 trace and the stomochord is then, to all intents and purposes, solid. 



The cavity of the pericardium contains a mass of loose cellular tissue chiefly 

 derived by proliferation from the ventral wall. The dorsal wall of the pericardium is 

 flat in front but soon becomes elevated into a hollow crest which meets and fuses 

 with the basement-membrane of the epidermis shortly in front of the coecal region 

 of the stomochord. 



The character of the stomochord changes in the vicinity of the coecal dilatation. 

 Its dorsal wall becomes elevated into a broad, rounded crest which projects into the 

 ventral wall of the pericardium. The lumen widens out in the centre of the dorsal 

 crest and gives off a median ventral diverticulum which forms the cavity of the 

 thickened ventral half of the stomochord. The cavity of this so-called ventral coecum 

 soon loses its integrity and is represented by numerous small disconnected cavities 

 which occur between the lateral pouches of the stomochord. 



The lateral pouches of the stomochord are very distinct structures. Each contains 

 a spacious cavity lined by well-defined columnar epithelium (except mesially where the 

 cavity is bounded by the body of the stomochord). The pouches tend to project for- 

 wards for a short distance as coecal pockets lying in a sheath of chondroid tissue. In 

 their middle portion the lateral pouches are separated by the sub-solid body of the 

 stomochord ; but more posteriorly their cavities communicate transversely, thus forming 

 the posterior portion of the ventral coecum which projects backwards into the cupule 

 of the nuchal skeleton (cf PI. XXXI. Fig. 38). 



Nuchal Skeleton. 



The ventral proboscis-canals come to an end posteriorly in the chondroid tissue, 

 without fusing together. This is another of the many points in which Spengelia show^s 

 relationship to Olandiceps. By their ending in this manner they make way for the 

 enormous keel of the nuchal skeleton. Thus their behaviour in this species is the 

 exact converse of what has been described above for Ft. flava. The large keel and 



