220 RESEARCHES IN HEI.MINTHOLOGV AND PARASITOLOGY. 



Length, lo to i8 mm.; thickness, 0.25 to 0.375 »ini.; tail, 0.12 to 

 0.24 mm. long. 



The oesophagus is long and cylindrical and is defined from the 

 intestine by a marked constriction. The intestine has a long trans- 

 lucent div-erticulum directed backward from its commencement, and 

 another more opaque directed forward along the opposite side of the 

 oesophagus. 



The Agamonoua of the Shad ranged from 15 to 25 mm. by 0.3 and 

 0.5 to 0.625 n^ni. in thickness, with the tail 0.125 to 0.25 mm. 

 In the smaller, translucent individuals the alimentary canal appeared 

 to be like that in the Aganionema of the Herring, but in the largest 

 individuals I am uncertain whether the condition is the same. 



The number of papillae to the head of Aganionema appears to be 

 three, but of this I could not satisfy myself. Wedl describes the 

 Agamo7iema of the Mackerel as having the mouth armed with a con- 

 ical tooth, which is capable of being protruded and retracted within 

 a sheath. (Sitzungsb. Akad. Wiss., 1855, 18, Taf. III. Fig. 24.) 

 In the worms under examination, I could see no such tooth, but to 

 one side of the mouth, as above described, a little conical spine fixed 

 by a spreading base, and commonly projecting obliquely forward and 

 outward. 



Ascaris adunca, Rudolphi. This worm was originally described as 

 a parasite of the Ituropean Shad, A/osa vuloaris. It is a frequent 

 though not a constant parasite of our Shad, and commonly appears 

 to occur few in numbers. From two to half a dozen were found in 

 three-fourths of the Shad examined. It occurs in the intestine, 

 pyloric appendages, and less frequently in the stomach. In general 

 appearance it resembles the Agavioyicma, but is readily distinguished 

 by its large lips. Its characters are as follows : Body cylindrical, 

 thickest posteriorly and tapering in advance ; caudal extremity in- 

 curved. Lips large and conspicuous, tail short, conical, acute. 

 Male with the caudal extremity spirally inrolled ; with a pair of 

 curved spicules. 



Female 12 to 40 mm. long ; 0.3 to 1.125 mm. thick ; tail 0.125 to 

 0.25 mm. long. Male, 20 to 30 mm. long, 0.45 to 0.55 mm. thick. 

 In the smaller individuals the body is more uniformly cylindrical or 

 less tapering in advance. This worm I formerly confounded with 

 its as.sociate Agamonema (Proc. Acad. Nat. Sci. Phila. , 1856, 55). 



Gymnoscolcx pida. — In all the Shad and Herring subjected to 

 examination there occurred a larva or scolex of a cestoid worm, 

 which, though closely resembling the Scolex poly worp/nis, I suspect 

 to be different, and have therefore given it another name. The lat- 



