481] LARVAL TREMATODES—CORT 35 



the striking changes made in the glands and all the tissues by the 

 extrusion of the cystogenous material (Figs. 33 and 34). The cysto- 

 genous glands in figure 34 have become much reduced in size, their cyto- 

 plasm is only slightly granular, and even their nuclei appear to have 

 shrunk. In fact they are distinguished only with difficulty from the 

 body parenchyma. The extruded material forms a layer about 0.0075 

 mm. in thickness, closely adhering to the animal. After the extrusion 

 of the cystogenous material the cercaria becomes somewhat shorter, 

 broader, and thinner than before. 



The mouth of Cercaria megalura is subterminal and the oral cavity 

 leads into a narrow prepharynx about the length of the oral sucker but 

 varying greatly with the state of contraction. The pharynx is small, 

 measuring on the average 0.022 mm. in length and 0.020 mm. in width, 

 and opens by a narrow passage into a much wider portion of the eso- 

 phagus. This soon divides into the narrow intestinal ceca which reach 

 almost to the posterior end of the body. The lining of the enlarged 

 portion of the esophagus and the intestinal ceca is formed by flattened 

 pavement cells with flattened nuclei, which are illustrated in figures 33 

 and 34. Figures 29 and 30 both show the relations of the digestive 

 system. 



At the posterior end of the body is found the pyriform excretory 

 vesicle which also has its walls formed of flattened cells with flattened 

 nuclei. From the anterior end of the vesicle pass forward two longi- 

 tudinal vessels which can be followed to the region of the pharynx 

 (Fig. 30). The excretory pore was not distinguished. In Cercaria dis- 

 tomatosa Looss (1896:200) described the excretory system as having a 

 short common trunk in the tail, leading from the bladder and opening 

 to the outside by two short ducts. Cary in his material of Cercaria 

 megalura located the excretory pore as dorsal just at the base of the 

 tail, and found no extension of the excretory system into the tail. The 

 most careful examination of the anterior part of the tail of Cercaria 

 megalura in living specimens, toto mounts, and sections showed no trace 

 of excretory tubules. 



The anlage of the reproductive organs (Fig. 30 ra) appears as a 

 small mass of nuclei just in front of the excretory bladder; from this 

 a line of nuclei extends forward to join another small nuclear aggrega- 

 tion just in front of the acetabulum. No definite outlines of organs 

 could be determined. The mass just anterior to the acetabulum repre- 

 sents to the ends of the reproductive ducts. 



In the literature are found descriptions of only two cercariae re- 

 sembling Cercaria megalura: Cercaria distomatosa Sonsino best de- 

 scribed by Looss (1896:197-204), and a cercaria from the Hawaiian 



