328 



ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



Fig. 1 c. Pt. ruficollis. Collar opened by ventral incision. The projecting knob at the 

 base of the proboscis is formed by the ventral coecum of the proboscis like the racemose 

 organ in Pt. flava. 



Fig. 1 (/. Sp. porosa. Similar view of macerated specimen. The alary processes and keel 

 of nuchal skeleton are seen as well as the cornua of the skeleton reaching beyond the middle 

 of the collar nearly to its posterior margin. 



The remaining figures on this plate refer to Pt. Jlava ; all sections are transverse 

 unless otherwise stated. 



Fig. 2. Section through base of proboscis at the level of the proboscis-pores. The 

 unequal size and wide openings of the pores may be noted. The section involves the free 

 edge of the ventral septum of the proboscis, and the cupule of the nuchal skeleton. The 

 dotted line in the epidermis indicates the line of demarcation between the nucleated and 

 fibrous (nervous) layers of the epidermis. 



Fig. 3. Portion of section through the region of insertion of proboscis into collar, passing 

 through the anterior neuropore. In this specimen the racemose organ (v.c) was slightly lobu- 

 lated. 



Fig. 4 a — c. Sections through collar nerve-cord (medullary tube) showing central canal 

 and hollow roots. 



Fig. 4 a shows the first root meeting the epidermis and the basal crest from which it 

 arises. 



Fig. 4 b shows the hollow neural crest between the first and second roots. 



Fig. 4 c shows the second root arising by constriction from the neural crest and meeting 

 the basement membrane of the epidermis. 



Fig. 5. Portion of section through the region of transition from collar to trunk, passing- 

 through the posterior neuropore (below which the dorsal vessel is seen) ; a collar-canal on the 

 left and a collar-pore on the right, opening into the first gill-pouch. 



Fig. 6. Section through the branchial region showing genital pleurae and lateral septa. 

 The gonads have been omitted from one side in order to show the lateral septum (which 

 is perforated by the genital ducts) more clearly. A tongue-bar is shown on the right side of 

 the figure, and a septal bar with cut ends of synapticula on the left side. 



Fig. 7. Section through the branchiogenital transition shortly behind the terminal gill- 

 slits, showing the postbranchial canal. 



Fig. 8. Inner view of the basal portions of three gill-slits. Reduced from the Quart. 

 Journ. Micr. Sci., Vol. 40, PI. 5, Fig. 3 ; it shows the wide tongue-bars and narrow septal 

 bars united by synapticula or cross-bar.s. 



Fig. 9. A group of gonads containing ova as seen in situ in the genital pleura, {ihid. 

 PI. 5, Fig. 5.) 



Fig. 10. Similar view of a single male gonad {Ibid. Fig. 4«.) 



Fig. 11. Nutritive bodies from gonads with darkly stained inclusions. The central body 

 of the smaller cell shows refringent contents. Zeiss Oc. 3, Obj. J, water imm. 



