456 PHORONIS 



" distributing " vessel, but also into a " recipient " vessel which 

 takes a course parallel with the former. The two recipient 

 vessels pierce the diaphragm, and after running for some distance 

 apart, fuse to form the efferent vessel, which continues down the 

 body on the left side of the oesophagus. At the aboral end of the 

 body the efferent vessel turns forward and becomes the afferent. 

 Both the main vessels give off numerous blood diverticula, which 

 are developed into plexiform sinuses on the walls of the stomach, 

 and in this region they are covered with the reproductive cells. 

 All the vessels are contractile, and Strethill Wright counted about 

 fifteen pulsations a minute. The blood contains numerous nucle- 

 ated, disc-shaped corpuscles differing in appearance from those of 

 the fluid in the body-cavity. The corpuscles contain haemo- 

 globin, which gives the red colour to the blood. 



The two nephridia or kidneys are essentially tubes which open 

 on the one side into the body-cavity, and on the other to the 

 exterior. The position of the external pores has already been 

 described, one being on each side of the anus. Each pore 

 leads into a tube which passes into that part of the body-cavity 

 situated below the diaphragm, where it divides, and each of the two 

 branches terminates in a ciliated funnel-shaped opening. The 

 smaller of these two funnels pierces the lateral mesentery and 

 opens into the lateral chamber, whilst the larger, whose opening 

 is very much drawn out longitudinally, opens into the rectal 

 chamber. The whole organ is ciliated internally. 



The nervous system lies in the skin immediately below the 

 epidermis. This position is very primitive, and forms one of the 

 most interesting anatomical peculiarities of the genus. The 

 nervous tissue is probably diffused all over the body, but there 

 is a special concentration or thickening in the form of a ring 

 which surrounds the mouth, following the base of the tentacular 

 spirals and giving off a nerve to each tentacle. The ring lies at 

 the outside of the base of the tentacles, the anus is not included 

 in it. Caldwell l has described in Ph. kowalevskii an asymmetri- 

 cal nerve-cord given off from the ring and running along the 

 left side of the body ; associated with which is a tubular struc- 

 ture of unknown function. In Ph. australis Benham mentions 

 two such tubes, one on each side of the body ; their precise value 

 is obscure. 



1 Proc. Roy. Soc. London, vol. xxxiv. 1883, p. 371. 



