330 ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



PLATE XXX. 

 Figs. 20 — 23 refer to Pt. earnosa. 



Fig. 20. Section through collar-canal. 



Fig. 21. Dorsal portion of section through region of transition from collar to trunk, 

 passing immediately in front of, and cutting tangentially the lip of, the posterior neuropore. 

 To the left of the point of junction of medullary-tube and epidermis is seen the posterior 

 end of the dorsal septum of collar. The collar canals are fused at one side with the wall 

 of the first gill-pouch on each side, and with the basal angles of the medullary tube at 

 their mesial sides. This association of collar-pores, first gill-pores and posterior neuropore 

 constitutes the posterior trematic complex of Enteropneusta (see p. 320). 



Fig. 22. Section through anterior branchial region, showing the absence of gonads and 

 the ventral coecum of the gill-pouch. On the left side the section passes through a tongue- 

 bar and on the right through a septal bar ; on the right of the figure the section is 

 diagrammatically made to pass exactly between two successive gill-pouches so that nothing 

 is seen of them. The thin layer of circular muscles which occurs outside the longitudinal 

 muscles is not shown in the figure. 



Fig. 23. Section through the branchiogenital transition shortly behind the terminal gill- 

 pores, showing the post^branchial canal (cf. PI. XXVIII. Fig. 7). 



Figs. 24 — 35 refer to Pt. ruficollis, n. sp. 



Fig. 24. Section through anterior end of central complex of proboscis in front of the 

 stomochord, showing the bifurcation of pericardium with the radial vessels of the glomerulus. 

 Between the two halves of the pericardium is seen the median septum of the proboscis, 

 containing dorso-ventral muscles. 



Fig. 25. Section through the dilated region of the stomochord with its lateral pouches. 

 Above the stomochord are seen the dorsal coelomic canals separated by the pericardium. 



The coelomic epithelium overlying the efferent vessels of the proboscis is ciliated. Above 

 the dorsal border of the pericardium are the two primary branches of the advehent dermal 

 vessel of the proboscis. Between pericardium and stomochord is the central blood-space ; 

 and below the stomochord are the ventral coelomic canals separated by the ventral septum 

 of the proboscis. 



Fig. 26. Section shortly posterior to preceding, showing the lateral pouches of the 

 stomochord uniting across the middle line to form the ventral coecum of the stomochord 

 which overhangs the ventral coelomic canals. On each side are seen the anterior rami of 

 the cupule of the nuchal skeleton. 



Fig. 27. Section through the region of the proboscis pore, showing the efferent vessels 

 lying in the scanty chondroid tissue and the alary processes of the nuchal skeleton arching 

 over the united ventral coelomic canals (ventral coecum of proboscis). 



Fig. 28. Section through region of anterior neuropore, i.e. through the region of the 

 insertion of proboscis into collar, showing the lobe-like ventral coecum of proboscis below 

 the keel of the nuchal skeleton. 



