BY WILLIAM A. HASWELL, M.A., B.SC. 269 



that the coeca possess the hydrostatic f unctioiis ascribed to the 

 swimming-bladder of Hesione. 



The Pscudoh(xmal System. 



The principal trunks of a pseudoha;mal system were observed 

 by Treviranus in Aphrodita, and the vessels in that genus wore 

 also noticed or described by Williams, Quatrefages and Selenka. 

 In the Polynoina, however, Claparede states that vessels are 

 altogether absent, and this statement is confirmed by Huxley 

 (Anat. of Invert.) as regards Polynoii squamafa. I have found a 

 pseudohffimal vascular system in five of this family, viz. : — Ayitinoe 

 Walii, Kinberg, Antinoe prceclara, mihi, Antinoe ascidiicola, mihi, 

 Polyno'e ochthccbolepis, mihi, and Thormora aryiis, Baird. It 

 presents dorsal and ventral contractile trunks, the former, which 

 is rather the larger, running along the middle line close under 

 the dorsal integument as far as the posterior termination of the 

 retracted gizzard ; the latter lying close above the nerve-cord 

 and running in the axis of the testicular or ovarian follicles, when 

 these are present. 



In Antinoe prceclara the dorsal vessel turns over to the left, 

 opposite the hinder end of the retracted gizzard and runs forward 

 parallel with the left border of the latter till it reaches the head 

 where it turns in again towards the middle line. The direction 

 of the peristaltic contractions is from behind forwards in the 

 dorsal vessel. Both dorsal and ventral vessels give oflt lateral 

 transverse branches corresponding in number to the segments. 

 All the vessels, even the principal trunks, have extremly delicate 

 walls and their contents are perfectly colourless, and these 

 characteristics may account in many instances for the failure to 

 detect their presence. In one case I observed in the fluid 

 amorphous, transparent, colourless corpuscles. In Thormora 

 aryus, which possesses a very opaque integument, through which 

 no trace of vessels can be seen, transverse sections reveal the 

 presence of psoudohgemal trnnks ; and it is not unlikely that a 



