306 LEIDY'S DESCRIPTIONS OF DISTOMA. 



detected ; I have usually found it in the abdominal cavity, the retractor muscles, the 

 olfactory sinus, or the substance of the foot. This is the most active of the three 

 stages, and during this period it contracts and elongates the body and changes its shape 

 into a variety of forms as are represented in figure 14, c — Jc. 



The distinctive features of the three stages are well marked, which principally are : 

 the caudal appendage to the first stage ; the posterior contractile sac communicating 

 with the exterior and the vascular canals in the second ; and the closed vascular 

 system and presence of circulatory vibrillse in the third stage. 



In the first stage the vascular canals are indistinct, but a principal vessel, on each 

 side of the body, passing forwards in a tortuous manner and then back again, are 

 readily observable. In the middle line of the body posteriorly I have observed the 

 outlines of a short apparent canal, which also appeared to communicate with an 

 excavation in the interior of the caudal appendage. In some instances the caudal 

 cavity was indistinct, in others it appeared to open exteriorly by an orifice 

 posteriorly. 



The intestinal rami are comparatively much more capacious than in the other 

 stages, and were filled with a finely granular matter, with yellowish corpuscles like 

 oil, measuring from I-5000th in. to l-3333d in., and minute spicular bodies from 

 l-3333d in. to l-1200th in. long, by l-10,000th to l-5000th in. thick. Among the 

 granular contents of the intestines in several instances I have observed from three to 

 ten nucleated organic cells, with granular contents measuring l-800th in. in diameter, 

 and recalling to mind the organic cells in the interior of the body cell of Grcgariiia. 



In the change from the first to the second stage the animal enlarges, the intestinal 

 rami become narrower and more tortuous, the vascular canals more distinct, the 

 central posterior short canal apparently becomes the contractile posterior sac of the 

 second stage, and the caudal appendage drops off leaving an opening at 'the posterior 

 part of the body communicating with the contractile sac. The removal of the tail is 

 gradual, it commences at the place of attachment to the body, by an absorption 

 anteriorly and posteriorly, so that it hangs by two peduncles one upon each side, and 

 resembles a cup suspended by two strings from the posterior part of the body. These 

 peduncles are next removed, and the tail is detached, and sometimes the animal is 

 observed with two pointed tubercles, one on each side of the posterior orifice of the 

 body, indicating the points of connection of the lateral peduncles. Occasionally I 

 have met with four of these prominences, arising from there having been four points 

 of absorption, after which for a short time the tail was suspended by means of four 

 peduncles. Sometimes the peduncle of one side only is detached, and the tail 

 remains hanging upon one side by the other peduncle as is represented in fig. 9. 



In the second stage the body is furnished with distinct transverse muscular bands, 

 a condition which was not distinguishable during the first stage. (Fig. 2.) 



