208 EDWIN LINTON. 



the anterior end meanwhile being bent ventrad and performing 

 a kind of pecking movement. This characteristic behavior of 

 the anterior end is plainly in part due to the jerking movements 

 of the posterior portions, and in part to the alternate protrusion 

 and retraction of a short, proboscis-like organ at the anterior end. 

 These movements suggest adaptations to enable the cercariae 

 to penetrate the soft membranes of the secondary host. In 

 some freshly liberated individuals a thin, hyaline, membranous, 

 fin-like border was distinguished. On one of these cercariae this 

 membrane was observed to be broken up into slender rod-like 

 processes which resembled long cilia. The posterior extremity is 

 divided into two slender branches. This forked extremity was 

 also seen to be surrounded by a thin membrane in some fresh 

 specimens. The structure of both body and tail is coarsely 

 granular. Rudiments of what probably represent the oral 

 sucker, and the pharynx were distinguished. When a sporocyst 

 is crushed, there are seen, in addition to the cercariae, of which 

 there may be many stages of development, some granular 

 material and balls of cells. 



While the prevailing shape of these sporocysts is long and 

 slender considerable variation exists. Both sporocysts and cer- 

 cariae are much like those found in the- annelid Hydroides dian- 

 thus. The cercaria resembles Cercaria cristata La Valette. 



3. Pearls. 



While the examination of numerous specimens of the edible 

 mussel {Mytilus edulis) resulted negatively, so far as trematode 

 larvae were concerned, a few cysts were noted, some of which may 

 have been caused by trematodes. At my request Dr. Irving A. 

 Field, who was opening large numbers of mussels in connection 

 with his study of the development, and experimental work on the 

 food value of this mollusk, handed to me those that in any way 

 appeared to be abnormal. The number of such was small. 



On July 24, 1909, 2 mussels were brought to me by Dr. Field, 

 which he thought to be in poor condition. They had been 

 cooked, so that there was no opportunity to examine them alive. 

 One of them had about 15 cysts from 0.5 to 2 millimeters in 

 diameter, a'ong the edges of the mantle, and 4 on the foot, 1.5 to 



