120 



THE PUR SEALS OF THE PRIBILOF ISLANDS. 



imijossible to state definitely whether these larvae represent the young of A. decipiens 

 or A. osculata. Mr. Lucas informs us that the seal occasionally, though rarely, eats 

 this species of cod, which is a deep swimmer and almost too agile for the seal, but 

 from the general structure of the worm, and from the fact that the seal does occa- 

 sionally eat this food, we are inclined to look upon it as one of the sources of infection 

 of the seal ascarid. 



The chief source of infection is probably the Alaskan pollock (Theragra chaloo- 

 gramma). In a specimen of this species taken off Popoff Island, which we owe to 

 the kindness of Mr. Barton Bean, of the U. S. National Museum, we have found 

 encysted nematodes which also agree essentially with the so-called " Ascaris cap- 

 sularia," and with the youngest forms found in the seal's stomach. 



We have, of course, not been able to make any direct infections, so that this 

 view that the Alaskan pollock and the Pacific cod form the intermediate hosts for 

 Ascaris decipiens is not absolutely demonstrated, but taking into consideration the 

 similarity of the encysted worms with the youngest worms found in the seal, and 



Fig. 21. 



Fig. 22. 



the fact that the seal feeds upon these fish, the probabilities in favor of the view 

 border upon a certainty. 



From the probable fact that the seals thus obtain their ascarid parasites from 

 their regular food, and from the fact that we are dealing in both cases with wild and 

 marine animals, it will be seen that nothing can be done to prevent infection. 



2. ASCARIS SIMPLEX Kudolphi, 1809, det. Krabbe, 1878. 

 Figures 23-29. 



f 1804, Asaaris simplex Eudolphi, Bemerkungen, etc., p. 94. Nomen nudum. 



? 1809, Ascaris simplex Eudolphi, Entozoorum hist, nat., II, ii, p. 170. — Eudolphi, 1819, Entozoorum 

 synopsis, p. 49.— Diesing, 1851, Systema helminthum, II, p. 155.— van Beneden, 1870, Bull. 

 Acad. roy. Belgique, 2 ser., XXIX, 363.— Cobuold, 1876, Proc. Zool. Soo. London, p. 297.— 

 COBBOLD, 1876, Journ. Linn. Soo. London, Zool., XIII, No. 65, Sept. 19, 1876, pp. 42-43.— 

 CoBBOLD, 1879, Parasites, p. 426.— Cobbold, 1886, Linn. Soo. Journ., XIX, pp. 176-177.— MoN- 

 TicELLi, 1889, Boll. Soo. Naturalisti Napbli, III, pp. 69-70. 



? 1819, Ascaris delphini Eudolphi, see p. 162. 



