346 WILLIAM NICOLL. 



obtained numerous examples from the same situation, and in 

 the only common gull (Larus can us) which I have had an 

 opportunity of examining an adult individual occurred in the 

 rectum. The habitat is invariably the bursa Fabricii and 

 the rectum, never the coeca or the intestine propei-. The 

 infection is not very numerous, there being seldom more 

 than a dozen parasites in one host. In several instances, 

 especially in young birds, examples of all sizes were found 

 ranging from small immature forms measuring '45 mm. to 

 fully developed adults over 4 mm. long. When removed 

 from the host the parasite displays considerable vitality, 

 several having been kept alive in distilled water over twenty- 

 four hours, and doubtless if a proper temperature were 

 maintained they would survive much longer. 



The general outline of the body is roughly oval, narrower 

 in front and rounded behind. In the extended state the 

 breadth is comparatively uniform, but on contraction a 

 characteristic shape is assumed, like that depicted in my 

 original representation of the species. Three well-marked 

 regions are then differentiated, a small head, a stout neck, 

 and a broad flat posterior part. The head is always distinct, 

 and possesses a raised ridge surrounding the oval sucker. 

 The ridge forms a shoulder-like prominence on each side of 

 the sucker, and its ends, which do not meet ventrally, are 

 tucked up towards the mouth. On the edge of the ridge is 

 a single row of regularly-arranged spines, about sixty in 

 number, and having a fairly uniform length of '037 mm. 

 The ant-acetabular region or neck is thick and muscular. 

 Its ventral surface is flattened and beset with numerous 

 strong spines ; the dorsal surface is more convex and devoid 

 of spines, except for one or two near the extreme edge of the 

 body. On the ventral surface there is a sort of ridge between 

 the genital papilla and the ventral sucker, which extends a 

 short distance round the sucker on each side. The post- 

 acetabular region is flatter and more delicate in structure. 

 It is not nearly so muscular nor capable of so much con- 

 traction as the ant-acetabular region. Its ventral surface 



