108 



shells, small stoues, pieces of calcareous Polyzoa, &c. If this is so, tliis species and 

 others possessing a similar tube must form a large portion of the sole's food. The 

 total number of specimens the contents of whose stomachs are recorded in the above 

 list is thirty-six. Of these eighteen, or 50 per cent., contained remains of marine 

 annelids (Chfetopods). If we add to these the number of specimens which contained 

 no remains of ChiEtopods but fragments of shells, probably derived from the tubes 

 of annelids, the number becomes twenty-eight or 77 per cent. Seven specimens 

 contained Ophioglypha alhida or other Ophiurid, or 19 per cent. One specimen 

 contained Synapta digitata, and one another Holothurian. Crustacea were present in 

 four specimens, or li per cent. In three specimens there were MoUusca probably 

 not derived from the tubes of Chsetopods, or over 8 per cent. Thus it is evident 

 that soles in their natural state feed chiefly on Ch^topods, and it is probable that the 

 bodies of these are rapidly digested, so that it is very difficult to identify the species to 

 which their remains belonged. 



Parasites. 



The common sole is remarkably free from parasites, which in many fishes occur 

 constantly in great number and variety. I have seen no internal parasites in the sole 

 except an occasional Nematode, or small thread-worm. Of external parasites the only 

 form I have observed is the Trematode, Phyllonella solece, whose structure has been 

 described at length in the preceding Section. This creature appears to do no harm to 

 the fish. I have never seen any signs of irritation or inflammation of the skin on which 

 numbers of the parasite were living. Sometimes as many as twenty or thirty specimens 

 of the parasite occur on a single sole. Phyllonella is, as I have described it previously, 

 hermaphrodite, but it does not fertilise its own eggs. I have not seen it in copula- 

 tion, but it may be inferred from the structure of the generative organs that two indi- 

 viduals copulate reciprocally, the penis of each being inserted into the uterus of the 

 other, and the seminal fluid received by each uterus passing up the oviduct to be 

 stored up in the spermathecte. Fertilisation of the ova then takes place after copu- 

 lation, and is effected by the spermatozoa which are expelled from the spermathecas 

 into the vestibule into which the ova pass from the ovary. The fertilised ovum, 

 too'ether with a quantity of yolk, is surrounded by its peculiar shell in the litems and 

 then the deposited ovum adheres by its filament to the skin of the sole. I have not 

 traced the development of the parasite, but have no doubt that it is direct, that the 

 youu" is hatched in a form closely resembling the adult, and immediately adheres by 

 its posterior sucker to the sole's skin. The parasite doubtless is nourished by the 

 mucus of the skin on which it lives, but how far its nutrition is effected by digestion of 

 the mucus within the smaU alimentary sac, and how far by direct absorption through 

 the surface of the body, it is impossible to say. The parasites spread from one sole to 

 another in all probability when the fish accidentally come into contact with one 

 another. 



