6 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.67 



tain. In the case of Ascarls decipiens {^^Porrocaecuin decipiens) 

 of the Alaskan seal, the source of infection with this parasite accord- 

 ing to Stiles and Hassall (1899) is to be found in certain fish that 

 constitute part of the food of the definitive host. Stiles and Hassall 

 (1899) say that immature ascarids, representing various stages inter- 

 mediate between the adult forms of Ascaris deHpiens and the so- 

 called Ascm'is capsularia^ which is a collective name applied to larval 

 nematodes found encysted in various species of fish, occur in the 

 stomach of seals, and that this suggests that these animals acquire 

 the infection with Porrocaecum decipiens as a result of eating in- 

 fected fish. Although Stiles and Hassall did not can-y out any 

 feeding experiments, they report finding encysted ascarids in the 

 Alaskan pollock and the Pacific cod, which were identical with the 

 youngest forms, presimiably of Porrocaecuiii decipiens^ found in 

 seals. Since these fishes are known to be eaten by seals. Stiles and 

 Hassall conclude with a fair degree of certainty that the definitive 

 host acquires the infection as a result of eating the intermediate 

 host. So far as concerns Ascaris incisa it was suggested by Leuckart 

 (1876) that it is the larval form of Ascaris depressa {z=Porrocaeciim 

 depressum)^ a nematode that occurs in various birds of prey such 

 as hawks and owls. Leuckart's view has been commonly accepted 

 by helminthologists, although no experimental evidence has been 

 obtained to prove this relationship. 



The occurrence of encysted Porrocaecum larvae in mammals sug- 

 gests a relationship between the intermediate and the unknown de- 

 finitive hosts similar to that described by Stiles and Hassall (1899) for 

 Porrocaecum decipiens. The unlaiown definitive hosts in the cases 

 reported by the present writer and by others are in all probability 

 birds, presumably hawks and oavIs, and other flesh-eating birds. 

 Two species of Poi^^ocaecuvv from hawks are represented in the Hel- 

 minthological Collections of the United States National Museum. 

 One species is from Circus hudsonicus and the other is from Falco 

 columbanvs., both from Fishers Island, New York. The form from 

 Circus hudsonicus has a very small intestinal cecum. An American 

 species of Porrocaecum is described by Smith, Fox, and White 

 (1908) as Ascaris ardea {=Porrocaecum retioulatum) according to 

 Baylis and Daubney (1922), from a North American blue heron 

 {Ardea herodias). Smith, Fox, and White fail to mention the ven- 

 triculus and the esophageal bulb, Baylis and Daubney (1922) are 

 convinced, however, that tlie species described by Smith, Fox, and 

 White is a synonym of Ascaris reticulata von Linstow 1899 (r=Pw- 

 rocaecuin reticulatum) . According to the former writers this species 

 has a well-developed intestinal cecum and a less conspicuous ven- 

 triculus, which they describe as short and oblong. While the larval 



