TREMATODE SPOROCYSTS AND CERCARI^. 207 



(figs. 3 and 5). This is probably the ovary. Behind the testes 

 on the median Hne is a dense granular mass which is doubtless 

 the beginning of the uterus. Granular masses which fill the 

 body, but are most dense along the lateral margins may represent 

 the beginnings of diffuse vitellaria. 



The cercariae of this species resemble Cercaria linearis Lespes, 

 but the sporocysts are different. 



2. Sporocysts and Cercaria from Pecten Irradians. 



Figures 7-10. 

 In the summer or 1909 I examined 361 scallops on nine dates 

 from July 3 to August 27 but found no sporocysts. In August, 

 1 9 10, I examined 6 large scallops from Ouisset Harbor. They 

 had been kept in a vessel of sea water in the laboratory for two 

 days before they were examined. After removing one valve the 

 animals were shaken vigorously in sea water. A few ■ small 

 sporocysts were found in the bottom of the dish in which the 

 scallops had been shaken. The scallops themselves were then 

 examined carefully for sporocysts but no more were found. The 

 sporocysts were elongate and slowly contractile with a tendency 

 to become arcuate. The larger examples at rest in sea water 

 measured 0.70 millimeter in length and 0.42 in breadth; length 

 of one of the smaller specimens 0.30, breadth 0.15. A specimen 

 compressed under a cover glass was 1.78 in length and 0.36 in 

 breadth. These sporocysts contained numerous slender, tailed 

 cercariae. One of the latter in alcohol was 0.40 in length and 

 0.024 in breadth; another, length 0.20, breadth 0.027, length of 

 body 0.085, length of tail 0.115. The first sporocyst examined 

 had what appeared to be an actively contractile papilla at each 

 extremity. These apparent papillae proved to be cercariae par- 

 tially liberated from the sporocyst, but evidently held by the 

 wall of the sporocyst contracting around them. All the cer- 

 cariae, both in the living and preserved specimens, are long and 

 slender, the tail, in all cases, except immature specimens, being 

 considerably longer than the body. In fully extended examples 

 the tail may be two or three times as long as the body. When 

 they are liberated from an active sporocyst they exhibit a pecu- 

 liar jerking movement of the tail and posterior half of the body, 



