WITH NOTES ON THE WEST INDIAN SPECIES. 



331 



The dorsal vessel is cut approximately at the point whence it is continued forwards 

 into the central blood-space, and where it gives off, dorsally, the advehent dermal vessel of 

 the proboscis. 



Fig. 29. Dorsal portion of section through the collar, showing the medullary tube, 

 somewhat flattened laterally, with central canal and solid root passing direct to the epidermis. 



Fig. 30. Dorsal epidermal portion of section through branchial region immediately behind 

 collar, showing the posterior ends of the collar-pores. On the left the second gill-pore is 

 cut tangentially and is seen to be overhung by the tongue-like fold of the collar canal. 

 On the right of the figure the section passes between the first and second gill-pores, and 

 shows the raphe in the middle of the tongue-like fold of the collar-canal (see Text). 



Fig. 31. Portion of section through branchial region, showing the gonad attached by a 

 genital duct to the epidermis at the outer side of the branchial gi'oove. 



Fig. 32. Section through the posterior end of the branchial region, showing the local 

 depression of the branchial grooves and reduction of the branchial portion of the gut. The 

 penultimate gill-pouches are seen at the bases of the grooves. At the outer and upper 

 sides of the grooves are seen the anterior portions of the lateral septa (close to their anterior 

 termination), enclosing the medial branches of the gonads. 



Fig. 33. Section shortly behind preceding, showing the anterior portion of the post- 

 branchial canal with its subdivided lumen, and below it a pair of grooves continued back 

 from the last pair of gill-slits. 



Fig. 34. Section through matvire ovarian ovum, showing refringent inclusions in the 

 nucleolus of the germinal vesicle. Highly magnified. 



Fig. 35. Ventral portion of section through hind-gut, showing the pygochord with its 

 vacuolated cells. 



PLATE XXXI. 



Figs. 36 — 45 refer to Spengelia porosa. 



Fig. 36. Central portion of section through proboscis in front of the central complex, 

 showing the vermiform i^rocess lying in the median septum, through which pass the dorso- 

 ventral muscles. On each side of the median septum is the central cavity of the proboscis, 

 the dorsal side of which is bounded by decussating conjunctive fibres. 



Fig. 37. Section through the commencement of the ceiitral complex, showing the anterior 

 projecting horns of the glomerulus, between which lies the vermiform process of stomochord. 



Fig. 38. Section through the posterior end of the dilated region of the stomochord, 

 shortly behind the glomei'ulus, showing the basal organs of the proboscis enveloped in 

 chondroid tissue. The epidermis is omitted. The lower division of the stomochord is the 

 ventral coecal dilatation, which projects backwards into the cupule of the nuchal skeleton 

 and so appears in section at this level separate from the smaller dorsal division. On either 

 side of the dorsal division of the stomochord are seen the dorsal coelomic canals [p), of which 

 the left is the larger in this region (on the right of the figure), and communicates at a 

 slightly anterior level with the end-sac, which is seen above the pericardium. The ventral 

 coelomic canals are nearing their termination in the chondroid tissue. 



