6-7 EDWARD VII. 



SESSIONAL PAPER No. 22a 



A. 1907 



X 



PRELIMINARY REPORT ON THE TREMATODES OF CANADIAN 



MARINE FISHE8. 



By J. Stafford, M.A., Ph. D. 

 (McGill University, Montreal.) 



The worms that live parasitically upon the surfaces or in the cavities or tissues of 

 our fishes may be distributed into six groups : — 



1. Turbellaria. 



2. Trematoda (Sucker worms). 



3. Cestoda (Tape worms). 



4. Nematoda (Thread worms). 



5. Acanthocephala (Hook-headed worms). 



6. Hirudinea (Leeches). 



Excepting the first, each of these groups is represented by numerous different 

 kinds as will be indicated in this brief account by the enumeration of the species of 

 Trematodes hitherto observed at the biological station, with an appended list of their 

 hosts. The Trematodes are commonly divided into (1) Ectoparasitic Trematodes', or 

 those that live on the skin or gills, and (2) Endoparasitic Trematodes, or those that 

 occupy some internal organ. The first are generally the more active, often possessing 

 such special sense organs as eyes; are well adapted, by flatness of form in the larger 

 species, and especially by the presence of suckers or hooks, to their habit of clinging 

 to the surfaces of their hosts; are most closely affiliated by organization with their 

 nearest relatives among free-living worms ; and develop from eggs by a direct and gra- 

 dual process' of growth. The second are generally more quiescent, having no special 

 sense organs; are more completely adapted to life in an internal organ; possess typi- 

 cally two suckers (sometime only one) and no hooks; and develop primarily from eggs, 

 but by a long, often complex series of transformations. The parasite during these 

 transformations lives at one stage in such an animal as a snail (intermediate host), 

 and at a later stage in a fish (final host) which has eaten the snail and in which the 

 worm now comes to full development and produces eggs. 



The life-histories of the species catalogued below are not known to me and are 

 matters for future research, but from what is known of others we may antici- 

 pate that the eggs of an ectoparasitic Trematode are deposited where it lives, on the 

 gills or skin of a fish. The embryos develop in the egg-shells or capsules which 

 finally burst, and then the young animals either remain on the same host or swim 

 about for a short time. In the latter case they may spread to new hosts, especially if 

 a school of fishes is in proximity, and settle down to the mode of life of their ancestors. 



With the endoparasitic Trematodes it is different. Each worm retains in its long 

 uterus an enormous number of eggs, only the first-formed or oldest of which are from 

 time to time deposited in the organ of the host occupied by the worm (intestine, gall- 

 bladder, urinary-bladder, &c., of a fish) and make their way out with the excrements. 

 When the eggs reach the sea water their contained embryos are already advanced in 

 organization, being provided with locomotory cilia and eye-spots ; and, upon bursting 

 the shells, are capable of spending a brief existence as free-swimming larvse (Mir- 



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