90 Part III. — Twenty-sixth Annual Report 



of the larvae greatly enlarged, while figure 6, Plate VI., represents a small 

 portion of the viscera crow^ded with the parasites and figure 7 on the same 

 plate shows a few of them separated out ; both of these figures are from 

 photographs enlarged about twice the natural size. 



Like most of the Entozoa mentioned in the preceding notes, these 

 parasites of the Porpoise are in their early stages probably migrants, but 

 little or nothing appears to be known concerning their life-history. In 

 Dr. Cobbold's opinion "it is highly probable that the embryos enter the 

 bodies of various fishes before they acquire sexual maturity. Thence they 

 will be passively transferred to the stomachs of cetacea, whence they bore 

 thtsir way through the tissues to the bronchi and pulmonary vessels," and 

 thus reach the goal of all their wanderings — an environment where they 

 can accomplish the purpose of their life, viz., the development of young, 

 on which in their turn will devolve the responsibility for their continuance 

 of the species. 



(3) On the Injurious Effects of Parasites on Fishes infested 



BY them. 



In the many cases of parasitism that have come under my observation, 

 I have usually been unable to notice any very serious results produced by 

 the presence of such unbidden and, perchance, unwelcome guests. 

 Occasionally evidence of injury apparently caused by them has been 

 obtained. 



Whitings and other Gadoids have been captured reduced almost to skin 

 and bone, having one or more large worm-like Lerncea hanging at their 

 gills full of the red blood they had extracted therefrom. Yet, even in cases 

 like these, it may be a moot point whether the emaciation is caused by the 

 Lerncea, or that their presence is simply oAving to the emaciated condition 

 of the fish — the emaciation itself being due to other causes — which by 

 reducing the fishes' vitality has left it more exposed to the attacks of 

 these parasites. But though there may be no direct proof that the 

 emaciated condition referred to was caused by these crustacean parasites, 

 their presence doubtless tended to aggravate the trouble, and the same 

 may be said about the attacks of parasites in other directions. The next 

 example of parasitism to which I have to refer shows how these vermin 

 (fishermen have a more suggestive name for them) may be injurious to 

 fishes in other ways. Figure 5, Plate VI., reproduced from a photograph, 

 represents the pectoral fins of a flounder infested with crustacean parasites, 

 Le'peophtheirus pectoralis. They are so numerous that a large portion of 

 both fins is covered by them. The soft tissues of the fins, more especially 

 round the edges and between the spiny rays, was extensively lacerated, 

 and this with the added encumbrance of so many beasts hanging on to 

 them must have interfered greatly with their movements. These parasites 

 are usually found adhering to the underside of the fins, and in this position 

 they are more sheltered and less likely to be rubbed off, and the irritation 

 they may produce will be the more exasperating. 



A careful scrutiny of the photograph shows considerably over a hundred 

 specimens of the Leqjeophtheirus adhering to the pair of fins ; they are so 

 crowded towards the outer edges of the fins that they overlap each other 

 two or three deep, and the delicate margin of the fins has been destroyed. 



