WITH NOTES OX THE WEST INDIAN* SPECIES. 329 



PLATE XXIX. 



Figs. 12 — 15 refer to Pt. flava. 



Fig. 12. Portion of section through hepatic region passing through an intersaccular 

 interval showing sacculation of ciliated groove of intestine. 



Fig. 13. Similar section passing through a liver- saccule. 



Fig. 14. Entire section through hepatic region involving a liver-saccule on the left and 

 an intersaccular interval on the right. 



Fig. 15 a — 6. Ventral portions of sections through caudal region to show the pygoehord 

 in its nioniliform and simple aspects. The dilated ventral border of the pygoehord abuts 

 upon the ventral vessel. 



Figs. 16 — 19 refer to Pt. carnota, a. sp. 



Fig. 16. Ventral portion of section through caudal region to show the narrow lamelliform 

 pygoehord. 



Fig. 17 o — c. Portions of sections through the region of insertion of proboscis into 

 collar, involving the posterior part of the proboscis end-sac (Eichelpforte). 



Fig. 17 a. Shortly behind the anterior neuropore, showing the end-sac lying below the 

 medullary tube. The lumen seen in the ventral wall of the end-sac is a diverticulum from 

 the main lumen. The body lying inside the sac is a tangential section through the duplicating 

 of the wall of the sac, described in the text. The section passes through the middle of the 

 coecal or pouched region of the stomochord ; above the ventrolateral pouches are seen the 

 forward prolongations of the cupule of the nuchal skeleton. 



Fig. 17 6. Section through the medullary tube posterior to preceding, showing the end- 

 sac opening by the proboscis-pore into the medullary tube (see Text). 



Fig. 17 c. Similar section still farther back, showing the coecal (post-trematic) extensions 

 of the end-sac. 



This section passes near the termination of the anterior transverse lumen of the medullary 

 tube, and a minute cavity, forming one of the system of separate medullary cavities into 

 which the primitive lumen is subdivided, is seen in the dorsal wall of the tube. 



Fig. 18. Portion of section through the collar-region, about half-way between the anterior 

 neuropore and the buccal orifice of the stomochord. It passes through the middle of the 

 nuchal portion of the stomochord, which is here fragmented into three divisions. 



The section also passes shortly behind the end of the ventral coecum (coelomic canal) of 

 the proboscis, and the alary processes of the nuchal skeleton have united behind the coelomic 

 canal to form the keel. The small dorsal moiety of the skeleton is the body. Below the 

 keel is a thick epithelial pad, projecting from the roof of the mouth (cf. PI. XXVIII. 

 Fig. 16). 



Fig. 19 a — 6. Dorsal portions of sections through the collar. 



Fig. 19 a shows the distal end of the first root entering the epidermis. 



Fig. 19 6 shows the proximal or basal portion of the first root close to the dorsal wall 

 of the medullary cord shortly in front of its origin from the latter; and the intra-epidermal 

 canal proceeding from the second root. The collar coeloni is seen to be traversed by radial 

 trabeculae enclosing radial muscles. 



45—2 



