SEA-FISHERIES LABORATORY. 283 



These encysted cercarise are the " spheroidal bodies " 

 of Alex. Monro*, figured by him as situated on the brain 

 and along certain cranial and spinal nerves. Their true 

 nature seems first to have been suggested by Sharpey in 

 1836, and later by IT. Goodsir (1844). But R. L. Madox,t 

 in 1867, seems first to have identified them with 

 Eudolphi's Distoma gracilescens, which is mature in 

 the gut of Lophius piscatorius. Madox apparently made 

 his identification by comparing the structure of his worms 

 with Cobbold's illustration of G. gracilescens. The 

 resemblance is striking enough to convince one of the 

 identity of the two worms, though, so far as I am aware, 

 the matter has not been proved experimentally by feeding 

 experiments. Madox gives the name Gasterostoma 

 neuronaia Monroii to his organisms. 



Lophius is, therefore, the final host of G. gracilescens 

 and various Gradidse — Gadus, Molva, Phycis, are the second 

 intermediate hosts. It is possible that the first inter- 

 mediate host may be omitted, but it is more probable that 

 it is to be found in some species of mollusc on which these 

 fishes may occasionally feed. 



Gasteivstomum, sp. (PL III., figs. 1-6 and 16). 

 (From the muscles of the plaice.) 

 A number of small plaice containing encysted mature 

 trematodes were obtained while trawling in Luce Bay in 

 October, 1904. These fishes were very abundant : in one 

 haul with a shrimp trawl about 150 small plaice were 

 obtained, and one-third or even more of these fishes were 

 infected. Only small plaice from about 2\ to 5 inches in 

 length contained the parasites, larger forms being appa- 

 rently free; also the smaller fishes were infected to a 

 relatively greater extent than the larger ones. 



* Structure and Physiology of Fishes, 1785, pp. 43 and 106. 



f Trans. Roy. Microscop. Soc. London, Vol. XV. (new ser.), pp. 87-99, 



PI. VIII., 1867. 



