1S02.] Zoology. 60 



Notice of Trematode Parasites in the Crayfish.— Prof. 



Charles A. Davis, of Alma, Michigan, has submitted to me tor 

 identification several cysts from the common crayfish, which prove 



the genus Distomum and are evidently -pecitieallv identical \viih~the 

 specimen described and figured bv K. Kanisav Wri-dit in volume 

 XVIII f the American Xa-itkaust, pp. 42!>— 4:in. Vrof. Wri-hfs 

 description is based on a single specimen which he obtained from a 

 cyst in the ovary of a crayfish. He referred it to the species DlMumnin 

 nodidonan Zcder. This species has been found in the cercaria sta-e 

 in Paludina impura by Von Linstovv. In the adult stage it is found 

 free in the intestinal canal of several European fresh-water fell < Terca. 

 Esox, Etc.,) and encysted on the outer surface of the intestine of one 

 (Acerina.) 



The specimens for the most part appear to be a little younger than 

 Prof. Wright's specimens, but the larger ones agree with it in every 

 .essential particular. The largest specimen observed, measured, when 

 freed from its capsule and straightened out, 04mm. in length. The 

 diameter of the head was 04mm. when seen in ventral view. The 

 neck was 03mm. in diameter. The body was contracted until it was 

 nearly circular in outline and measured Cr6mm. in breadth. The head 

 bears six papillary appendages. Two of these are latei il one 1 t 

 triangular in shape and project from the anterior edges of the sucker. 

 In the largest specimen observed these measured about 0-2mm. in 

 length. The other four papillae lie on the antero-dorsal side of the 

 head. They are flattish, bluntly-rounded, 04mm. broad and 0-lomni. 

 in length. The oral sucker is considerably larger than the ventral. 

 The former is about 0'3mm. by 0*2mm. in its two diameters, the antero- 

 posterior diameter being the longer. The latter is 02mm. in its 

 transverse diameter and a little less than this in its antero-posterior 

 diameter. In another specimen the anterior sucker was 0*36mm. long 

 and 0"3inm. broad, and the ventral 0-2mm. long and 0"24mm. broad. 

 The testes are about 0'2mm. in length. The anterior end of some of 

 the smaller specimens appears to be invaginated. 



The cysts are globular. Each specimen when freed from its con- 

 nective-tissue shell, is found to be enclosed in a thin pellicle. The 

 diameter of the pellicular cysts is, in most cases, about 0'5mm. 



Prof. Wright states in the article alluded to above, that the struc- 

 ture of the mouth sucker of his specimen is not entirely in accordance 

 with Von Linstow's description. While my specimens agree so closely 

 with Prof. Wright's that I have no hesitation in regarding them as 



