94 PEOF. W. J. DAKIN ON A NEW SPECIES OF 



of the proboscis (PI. 11. fig. 8, Ch.T.), and sometimes the canal leading to 

 one of the proboscis pores is missing for a space, the chondroid tissue 

 taking- its place (fig. 9, Ch.T.). 



The chondroid tissue when highly magnified is distinctly fibrous. With 

 hsematoxylin and eosin it often stains like the blood in the central blood- 

 sinus. Its structure differentiates it at once. Every here and there are 

 cavities, in which lie small fusiform nucleated cells. It is assumed by 

 Spengel and Willey that the cells of the chondroid tissue arise chiefly from 

 the epithelium of the dorsal coelomic canals. This is probably the case, 

 but the cells found enclosed in the chondroid tissue are, to my mind, part 

 of the tissue itself, and responsible for its production. 



Vascular System. 

 Prohoscis glomerulus. — The glomerulus, like that of Glossobalanus minutus 

 and Balanoglossus australiensis, extends over, and forms a cap to, the 

 pericardium and the stomochord (PI. 10. fig. 2). Posterior to the end of the 

 stomochord, the glomerulus becomes restricted to two lateral masses lying- 

 one on either side of the central complex of the proboscis (fig. 4, rad.glom.). 

 The cells of the splanchnotheca are easil}^ recognised, covering the glomerulus 

 distally (fig. 4, SpL). There is little to add in the way of details. The 

 general arrangement of the blood-spaces is similar to that already described 

 in other Ptychoderida3. The efferent proboscis vessels (figs. 5 & 8, JEf. V.) 

 cannot be recognised anteriorly to the proximal end of the glomerulus. 

 They are not only in connection with each other by blood-spaces situated in 

 the chondroid tissue, between the body and keel of the proboscis skeleton, 

 but they enter into communication with the capillary network of the 

 proboscis. This condition was first described by Hill in Balanoglossus 

 australiensis. It is probably to be met with in other species of the 

 Ptychoderidse. 



Pericardium. 



The pericardium (PI. 10. figs. 2 & 4, PI. 11. figs. 5 & 9, Per.) has the 

 same essential structure as in the other described species of Ptyclwdera. It 

 extends anteriorly just as far as the stomochord. Dorsally it is connected to 

 the integument for some distance, thus forming a dorsal hollov\^ septum in 

 the proboscis (fig. 5). This contact with the integument of the proboscis ends 

 at about the plane of the lateral caica of the stomochord. The ventral wall of 

 the heart-bladder is convex, owing to the space underlying it being occupied 

 by the central blood-sinus (figs. 2, 4, 5, & 8, C.h.s.). There is, however^, no 

 infolding of the pericardium as in Balanoglossus australiensis. The cavity of 

 the pericardium is almost filled with cellular tissue which extends right to the 

 distal end of this organ. There is practically no difiPerence in the appearance 

 of this cellular tissue throughout the pericardium. The same transverse 



