ABT. 1 TREMATODE PARASITES OF BIRDS LINTON 13 



Larus marinus. 



Woods Hole, Mass. : Larus argentatus^ L. atricilla, L. delawarensis, 

 L. 77iarinus, L. Philadelphia, Colymhus auritus, 0. hoIholU, Gavia 

 immer, intestine. 



These distomes from the intestines of iBve species of gull, two 

 species of grebe, and the loon appear to be the same species as that 

 described by N. C. Gilbert from the loon.^ They agree in the fol- 

 lowing characters : Oral sucker small, head renif orm, surrounded by 

 a single circle of spines interrupted on the dorsal side. The number 

 of spines in the oral circle is 22, and they are of nearly equal 

 size, length 0.065 to 0.07, breadth 0.015 to 0.020. The postero-median 

 spines on each side are a little smaller than the others. Neck and 

 anterior part of the body spinose ; neck, except in relaxed and partly 

 macerated specimens, rather short and more or less tapering; body 

 usually nearly linear, but in some cases thickening in the vicinity of 

 the testes or ventral sucker. There is a short prepharynx ; pharynx 

 longer than broad, its length approximating the diameter of the 

 oral sucker; esophagus longer than pharynx; intestinal rami begin 

 a short distance in front of the ventral sucker and extend to the 

 posterior end of the body; ventral sucker from two to three times 

 the diameter of the oral sucker. Testes two, following one another, 

 either contiguous or separated, and either oval-elliptical, quadri- 

 lateral, or subtri angular in outline, depending on age and condition. 

 In many cases the first testis is quadrilateral and the second sub- 

 triangular. In a few cases the testes were slightly diagonal, appar- 

 ently not due entirely to distortion of the body. Those cases in 

 which the testes were oval-elliptical, and separated from each other, 

 were more or less flaccid, some of them even showing signs of macera- 

 tion. They had lost both oral and body spines. The cirrus-pouch 

 and seminal vesicle are short and at the antero-dorsal surface of the 

 ventral sucker. The ovary, usually subglobular, is a little way in 

 front of the first testis, from which it is separated by a short space 

 in which lie the transverse yolk reservoir, the shell -gland, and the 

 beginning of the uterus. The uterus lies between the ovary and the 

 ventral sucker. Ova not numerous, in balsam measuring from 0.081 

 to 0.09 in the longer, and from 0.048 to 0.054 in the shorter diameter. 

 The vitellaria are massed in the posterior end of the bod}^, which is 

 more or less elongated, behind the testes, and extending forward, in 

 some cases not beyond the posterior margin of the second testis, in 

 others extending to different levels on one or both sides of the testes, 

 but not extending in front of the first testis. In older individuals 

 there is a clear space on the median line back of the testes separating 

 the vitellaria into two lateral masses. In young, robust individuals 



^ Occurrence of Echinostomum spliiulosum Rndolphi, Amer. Nat., vol. 39, pp. 925-927. 



