182 



Part III. — Eighteenth Annual Report 



List of Fishes ox which Parasites have been Found — continued. 



Scientific names. 

 Plenronectes flesus, Linn. 

 So lea vulgaris, Quen. 

 Salmo salar, Linn. 

 Salmo truita (Flem.). 

 Clupea spraffus, Linn. 

 Clupea finta. Linn. 

 Conger vulgaris, Cuv. 

 Orthagoriscus mola, Linn. 

 Galeus canis, Linn. 

 Lamna cornubica, Cuv. 

 Scyllium canicula, Linn. 

 Raia batis, Linn. 

 Rata clavata, Linn. 

 Rata oxyrhynchus, Linn. 

 Raia fullonica, Linn. 

 Raia circularis, Couch. 



Common names. 

 The Flounder. 

 The Sole. Black Sole. 

 The Salmon. 

 The Sea-trout. 

 The Sprat. 

 The Twaite Shad. 

 The Conger. 

 The Short Sun-fish. 

 The Tope, or Toper. 

 The Porbeagle Shark. 

 The Lesser-spotted Dog-fish. 

 The Skate. Grey or Blue Skate. 

 The Thorny. Thornback Skate. 

 The Long-nosed Skate. 

 The Shagreen Ray, Fuller's Ray. 

 The Cuckoo Ray, Sandy Ray. 



The number of fishes in this list is forty-seven. The majority of them 

 have yielded one or two kinds of parasites only, while on a few as many 

 as four and five different species have been obtained. The grey skate 

 has yielded the largest number of parasites of any of the fishes examined, 

 six different kinds having been found on specimens of this species. They 

 comprise Caligus curtus, Trebius caudatus, Chondracanthus annulatus, 

 Charopinus dalmannii, Lernceopoda sp , and Cirolana borealis. The 

 saithe and the torsk come next with five species each. The hake and 

 the toper have yielded four, while three each have been obtained on the 

 common gurnard, the halibut, the turbot, the plaice, the conger, and 

 the sun-fish. Eleven fishes have yielded two, and twenty-six only one 

 species of parasite each. 



Concluding Remarks. 



The study of the distribution of these organisms is still being continued, 

 and their habits and development will also form subjects of research as 

 opportunities occur. It is probable that there is scarcely a fish within the 

 Scottish seas, as there doubtless is in other seas, which does not at one 

 time or other during its life harbour one or more crustacean parasites, and 

 this itself furnishes a sufficient reason for the study of these creatures, and 

 in this study more than one interesting problem is still awaiting solution. 

 For example, we find, on the one hand, a species such as Caligus curtus, 

 which seems to have no limit to the number of fishes from which to 

 choose an associate for itself ; on the other hand, we see a crustacean, 

 such as Lernwopoda bidixralis, which appears to be limited not only to 

 a particular kind of fish, but also to a particular part of that fish. The 

 interest in the difference between these two forms is increased when it is 

 remembered that both in their early stages of life are free-swimming, and 

 that they live in a medium which is favourable to their dispersal over a 

 wide area ; moreover, there are fishes of various kinds passing from time 

 to time within easy reach of both during their free-swimming stages. 

 How comes it, then, that in the one case the limit of existence in the 

 adult is so greatly circumscribed, whilst there is almost unlimited scope 

 in the other 1 



There is, of course, a possible explanation which might to a certain 

 extent account for the difference 1 have alluded to, and that is that the 

 difference is the product of the habitat ; in other words, that the animals 



