112 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Fixation plays strange tricks with the appearance of these 

 organs, and sometimes they are widely expanded, with 

 almost invisible walls, while at other times their lumina 

 are reduced to the merest chinks, and the walls may be 

 quite thick. 



The situation of the worm is also unusual. As a 

 rule a Tetrarhynchid larva inhabits the body cavity, but 

 it is enclosed in a cyst, derived partly from the. larval, 

 partly from the host's tissues. Coenomorphus, however, 

 lives freely in the peritoneal cavity attached by means of 

 its suckers and hooks in the manner of an ordinary 

 Cestode. 



What we doubtless have here is a "permanent" 

 larval stage. Gadus virens is, for C'oenoinorphus, a 

 collateral host, not a true intermediate host. I have argued 

 elsewhere* that this is the nature of the Teleostean 

 hosts of T etrarhynchus einnaceus, which Cestode inhabits 

 only the Rays in its adult condition, but a number of 

 Te]eosts in the plerocercoid stage. It is difficult to 

 believe that the Ray is infected by eating such fishes as 

 Gurnards and Whiting, in which fishes plerocercoid 

 larvae of T. evlnaceus are, in my experience, always 

 found. The true larval host is no doubt some small 

 invertebrate, a mollusc or crustacean, and both the 

 Teleosts and Elasmobranchs are infected by eating these 

 creatures. The plerocercoid and adult stages are, on this 

 view, collateral ones, as are the hosts. The same view is 

 also taken by Southwell with regard to the life history 

 of T etrarhynchus unionif actor , which inhabits both 

 Teleosts and Elasmobranchs in Ceylon waters. But the 

 Teleost in this case is, according to Southwell, a cul-de- 

 sac in the life-history. 



Coenomorphus is therefore probably a Tetrarhynchid 

 ^Parasitology, Vol. IV, No. 4, January, 1912, p. 368, 



