196 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



considerable moment, and it is desirable that our knowledge of the life-history of the 

 species should be extended. There is some reason for thinking that the final host is 

 a fish-eating bird, although it may be some voracious fish, like the gar. 



Dr. H. B. Ward has published some very interesting notes of his observations on 

 the fish parasites of the Great Lakes (No. 18). From an examination of 20 species of 

 lake fish, the total number of individuals examined being 102, 95 of which were 

 infested with parasites, he obtained something over 4,000 Trematodes, 2,000 Acan- 

 thocephala, 200 Cestodes, and about 200 Nematodes. Trematodes were obtained from 

 every species examined, and in enormous numbers from the dogfish (Amia calva). 

 Cestodes were obtained from 14 of the 20 species, Acanthocephala from 13, and Neina- 

 todes from 7. Dr. Ward describes a new Distoma from Amia calva (No. 19,) encysted 

 forms of which he finds in the crayfish (Cambarus propinquus), thus establishing its 

 life-history. The adult form was found also in the channel catfish, Ictalurus puncta- 

 tus, and the yellow perch, Percaflavescem. 



I would conclude from the results of Dr. Ward's researches, as compared with what 

 I have had the opportunity to observe, that Trematodes are relatively much more 

 abundant in fresh-water fishes than in marine fishes. 



CESTODA.i 



My investigations have been mainly on marine fishes, in which I have found the 

 members of this order very abundant, largely, perhaps, because of the predilection 

 which the adult forms appear to have for the spiral valve of the Elasmobranchii. The 

 individual shark or skate is not only an engine of destruction, but a source of infec- 

 tion from which innumerable ova of a variety of cestode parasites issue to become 

 encysted in various animals which serve them for food. There can be little doubt 

 that if the sharks and skates were to be exterminated, or sensibly diminished in num- 

 ber, the aggregate of intermediate parasitism among the teleosts, squids, Crustacea, 

 and other food of sharks and skates would be materially lessened. The destruction 

 of the Elasmobranchii, while probably not practicable, would be a disturbance of the 

 balance of nature wholly in favor of the food-fishes. 



I find larval forms of two genera (Rhynchobothrium and Tetrarhynchus), in which 

 the adult forms are peculiar to sharks and skates, very commonly encysted in many 

 spr. M>s of marine food fish, such, for example, as the squeteague ( Gynoscion regale). 

 Of adult forms, while the genus Dibothrium is somewhat abundant in cods (Oadidcc) 

 and flounders (Pleuronectidcv), and tapeworms not unusual in the eel and some fresh- 

 water fish, the vast preponderance is to be found infesting the Elaxmolmincliii. The 

 case of the IHbothrium of the Rocky Mountain trout has already been mentioned. 



It is very desirable that our knowledge of this important group of parasites be 

 extended, both in the direction of ascertaining what forms are to be found in the fish 

 of our waters and in working out the life- hi stories of forms already known. It should 

 be remarked that one species of human tapeworm (Bothriocephalus latus) is believed 

 to be got from eating the flesh of the European tench. 



I take this opportunity of calling attention to a paper by Dr. F. S. Monticelli 

 (Boll. d. Soc. d. Nat. Napoli, Serie I, vol. vin, Anno vm, Fasc. 1, 1894) Si Mangiano 

 le Ligule in Italia? In this paper the author affirms that Leuckart is in error in stat- 

 ing (Die Parasiten des Menschen) that in Italy the ligula a larval form of a cestode 

 worm which develops in the abdominal cavity of certain fresh-water fish and there 



1 See List of Authorities : NOB. 7, 8, and 10 to 16. 



