100 THE FUB SKALS OF THE PRIBILOF ISLANDS. 



in the death, rate of pups too young to catch fish, and a crowded condition of the 

 rookeries is of no importance in connection with the spread of infection. There is 

 evidently no way open to prevent infection. Asoaris decipiens was collected by Lucas 

 from the fur seal, the hair seal, and the sea lion; and A. osculata from the sea lion 

 (p. 105). These same worms are found in other parts of the world (Greenland, etc.) in 

 other hosts. 



The Ascarides of marine mammals. — Under this head we discuss the history of 

 the subject, the division of the genus, and the history and structure of all of the 

 various forms described. 



III. — Family Strongylidae; (p. 164), subfamily Sclerostominae; genus Uncinaria. 



A few worms of this genus were found by Lucas in a fur-seal pup, three months 

 old, but our material is not sufScient to perpait a detailed study of the form. The 

 worms of this genus are blood suckers of the worst type, and a heavy infection would 

 undoubtedly have very serious effects upon the pups, as allied worms do upon man, 

 dogs, cats, and other animals. The life history of and source of infection by the seal 

 Uncinaria is not demonstrated, and can not well be demonstrated at this distance from 

 its habitat, but analogy would point at a direct development without an intermediate 

 host. (See also Supplementary Note, p. 165.) If this view drawn from analogy is • 

 correct, the infection would take place upon the rookeries, and a crowding of the 

 ropkeries with an open season and lack of nourishment would give the conditions 

 necessary for an epizootic; thus this worm might under conditions play an important 

 role in the mortality of the pups,more especially if the latter were deprived of nourish- 

 ment from their mothers because of pelagic sealing or other causes. 



IV.^Family Bothriocephalidae (p. 167;) subfamily Bothriocephalinae; genus 

 Bothriocejphalus. A few wotms of this genus were collected from the fur seal by Lucas 

 who states that about 40 per cent of the seals are infected with them. Lack of time 

 prevents our making a detailed study of the form. Analogy points to fish as the 

 intermediate host, and hence as source of infection. These worms would accordingly 

 not be found in young pups. 



V. — Compendium of parasites arranged according to their hosts. 



VI. — Bibliography. 



I.— INTRODUCTION. 



The earliest record we have been able to find of parasites in the marine mammals 

 of Bering Sea is a statement by Steller (1751') that in July, 1742, he found some 

 parasitic worms about half an inch long in the stomach of the now extinct sea cow, 

 Hydrodamalis Stelleri. These helminthes {Ascaris rytinae, see p. 163,) are now uniden- 

 tifiable, but have been referred to by various helminthologists. 



In helminthological literature we have not succeeded in finding any further 

 references to parasitic worms in Bering Sea, and especially of the fur seal, but Mr. 

 Lucas has called our attention to the following passages in other works. 



Elliot (1882,' p. 35) in. his Monograph of the Sea Islands of Alaska, refers to 

 worms in the stomach of the fur seal and the sea lion as follows : 



I have examined the stomachs of hundreds which were driven up and killed immediately after 

 their arrival in the spring near the village; I have the word of natives here, who have seen hundreds 

 of thousands of them opened during the slaughtering seasons past, but in no one single case has 



'The dates enclosed in parentheses refer to the works cited in the bibliography, pp. 171-174. 



