MUSSEL, FAUNA OF MAUMEE EIVER. 65 



In the reservoir of the feeder canal at Fort Wayne we found an 

 Anodonta plentifully infected with these sporocysts, and were able 

 to make out in detail some of the steps in the life history of the 

 animal. 



The sporocysts were small white objects, elliptical in outline, about 

 1.14 millimeters in length and 0.05 millimeter wide. The skin of the 

 sporocysts was transparent enough to reveal, in the interior, the cer- 

 cariir, which were three in number in most cases examined, closely 

 doubled up and snugly packed together, and performing an uneasy 

 wiggling motion. The walls of the sporocyst easily rupture; in an 

 example studied at St. Paul the previous year the covering was torn 

 apart by a dissecting needle and the cercarian set free. In the ex- 

 ample now under discussion the sporocysts were rupturing of their 

 own accord, allowing the cercarine to escape. The following is a de- 

 scription of the various stages observed : 



Cercaria just escaped from the sporocyst: 



Body elongate cylindrical with bluntly rounded ends and divided 

 by a well-defined constriction into an anterior two-thirds, the body 

 proper, and a posterior one-third, the " tail." Body portion ellip- 

 tical in outline with the two ends similar. Anterior sucker terminal, 

 about one-fourth the greatest body diameter, circular, with concen- 

 tric ridges faintly marked. 



Posterior sucker one-third body diameter, also circular, but with 

 radiating ridges, situated almost in the exact center longitudinally 

 as well as transversely ; constriction only one-seventh the body diam- 

 eter with a well-defined groove all the way around. Posterior por- 

 tion (tail) almost perfectly elliptical, twice as long as wide, both ends 

 alike and more bluntly rounded than the body proper. Tail covered 

 with a thick epidermis, raised into longitudinal ridges close together, 

 very narrow and zigzag in arrangement. 



The internal structure is indistinct, but far enough developed to 

 distinguish the pharynx and digestive canals. The former is rela- 

 tively smaller than in the adult and is much nearer the posterior 

 sucker than the anterior one. This means that in after development 

 the posterior sucker travels backward, while the pharynx travels 

 forward. At this stage the whole interior of the body is filled wdth 

 large cells having numerous and interlacing intercellular spaces. 



After remaining under the cover glass for a little time the tails 

 break off at the constriction and the body moves about alone. 



The following is a description after the tail is shed : 



Body elongate, ovate, without any traces of segmentation or sepa- 

 ration into parts; anterior end evenly rounded, posterior end drawn 

 out into a point, bluntly rounded at the tip. 



Anterior sucker terminal, circular, three-sevenths the diameter 

 of the body, with circular ridges. Posterior sucker on the mid line 



