326 



ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



te. Truncal canal. 



th. Throat and wall of throat (collar-gut). 



fm. Transverse muscles. 



if. Ventral coelomic canals and coecum of proboscis. 



rii. Ventral nerve-cord. 



vp. Vermiform process of stomochord. 



vrv. Ventral recurrent dermal vessel of proboscis. 



vs. Ventral septum. 



ri\ Ventral vessel. 



PLATE XXVI. 



All the figures on this plate refer to Pt. flava. 



Fig. 1. Dorsal view of normal specimen with genital pleurae divaricated and exposing 

 the free pharynx, x 3. 



Fig. 2. Similar view of anterior portion of macrobranchiate variety with fully expanded 

 genital pleurae. The oval bodies disposed in zones on the inner surface of the genital 

 pleurae are glandular dermal islets, x 3. 



Fig. 3. Similar view of braehybranehiate variety. The genital pleurae are closely 

 approximated in the branchial region so as to cover in the pharynx. The hepatic tract is 

 sharply defined, the saccules being arranged like the leaves of a book, x 6. 



Fig. \. Anterior end of specimen from which the whole of the pre-nuchal region of 

 the proboscis had been removed, showing the central complex projecting freely as a rigid 

 body, hard to the touch, x 3. 



Fh;. 5 A — E. The anterior ends of a series of regenerating individuals from the dorsal 

 side (except £"-'). 



A. The medullary folds are wide apart, exposing the base of the collar nerve-cord 

 throughout its entire length. The triangular body seen at the base of the collar groove in 

 its anterior half is due to the vaulted floor of the groove (cf. PI. XXXII. Fig. 66). The 

 hepatic saccules commence at h and the entire pre-hepatic portion of the specimen measured 

 3 - 25 mm. in length. 



B. The medullar}' folds are still open but closely approximated. At the anterior end 

 they are fused (see PI. XXXII. Fig. 68). Proboscis + collar = 3-5 mm. 



0. A rudimentary proboscis and collar have been added immediately in front of the 

 hepatic region, x about 4. 



D. The medullary folds have completely closed over the collar nerve-cord, but there re- 

 mains a deep dermal groove in the posterior half of the collar in the middle line, x about 3. 



E 1 and E"-. A regenerating individual from dorsal and ventral aspects to demonstrate 

 the homodynamy of the zones of the collar with the annulations of the trunk, x about 4. 



