106 THE PUE SEALS OF THE PRIBILOF ISLANDS. 



Since Schneider's monograph appeared, various authors have studied the nema- 

 tode parasites of marine mammals; some of their articles are worthless, as they show 

 a complete ignorance of the literature of the subject as well as superacial study of 

 the worms. The most important studies upon the subject have been made by Krabbe 

 (1878) and Jagerskiold (1894), whose writings will frequently be referred to in the text 

 of this report. 



Before passing to a description of the worms to be studied, it will be necessary to 

 consider for a moment the classification of the genus Ascaris. 



Various attempts have been made to divide this genus into subgenera and sections. 

 The divisions made by earlier authors, Eudolphi (1809), and de Blainville (1828) need 

 hardly be considered here. 



Dujardin (1845) proposed a division based upon anatomical characters, and this 

 classification, although not generally accepted, should be given here because of its rela- 

 tion to some of the forms which occur in marine mammals. The following table shows 

 the various groups proposed by Dujardin. 



I. Subgenus Aacaris : Uterus with two parallel branoheB extending caudad. 



1. Section : Oesophagus simple, with or without ventricle, but without pyloric (caeoal) append- 



ages. This section, with 54 species, included the type of the genus and Ascaris osculata 

 Eudolphi (see p. 151). 



2. Section : Oesophagus followed by a more or less distinct ventricle, with oesophageal caecum, 



or with an intestinal pyloric appendage. Species Nos. 55 to 66, none of which are considered 

 in the present report. 



3. Section : Oesophagus prolonged by a caecum or pyloric appendage at the side of the intestine, 



and accompanied also by another caecum from the intestine and directed cephalad. Species 

 Nos. 67 to 71, none of which are considered in this report. 



4. Section: Oesophagus with a single caecum or pyloric appendage extending candad at the 



side of the intestine. One species, A. acus. 

 II. Subgenus Asearidia : Uterus with two branches extending in opposite directions. Species Nos. 

 73 to 75, not considered in this report. 



III. Subgenus Jnisafcjs ; Male with two unequal specnles. See A. Dusaumierii, p. 161. 



IV. Subgenus Polydelphia : Uterus divided into more than two branches. Type and only species, A. 



anoura. 



Investigations since Dujardin's time seem to prove that this classification can not 

 be accepted. 



Schneider (1866) proposed to divide the genus Ascaris as follows: 



A. Lips with dentigerous ridge, but without intermediate lips. 



B. Lips with dentigerous ridge and with intermediate lips. 



C. Lips without dentigerous ridge, but with auriculae and intermediate lips. 



D. Lips without dentigerous ridge, with " Loffeln" and intermediate lips. 



The importance of the intermediate lips as a means of classification seems to be 

 well established, and will be adopted in this report. 



As stated above, a study of the ascarides collected by Lucas necessarily led to a 

 study of all of the ascarides found in marine mammals, since it immediately seemed 

 probable that the parasites from Bering Sea were closely allied to the forms collected 

 from allied hosts from Greenland and Iceland. Unfortunately we have had very little 

 material for comparison, and have not had time to obtain for consultation any of the 

 types contained in the European collections.' Our determinations are therefore based 

 entirely upon the diagnoses of other workers. 



' See pp. 113, 126, 134, 142, 157. 



