490 University of California Publications in Zoology [Vol. 18 



moving. A few of the original lot are still alive, having lived more 

 than a year in an aquarium. Since only a small percentage of these 

 snails were infected with cercaria of the Japanese blood fluke, the 

 material available for study was small. To make sure that the cercariae 

 found in the snails belonged to S. japonicum, two white rats were 

 infected through the skin. Post-mortem examination of these rats 

 made six weeks later revealed specimens of S. japonicum. On account 

 of the limited amount of material no extensive infection experiments 

 or studies of the developmental stages between the cercariae and the 

 adult were attempted. In all, sporocysts and cercariae from five 

 infected snails were utilized in this study. 



METHOD OF STUDY 



The greater part of my observations of the cercaria of S. japon- 

 icum were made from living specimens. The method used in this 

 study of the living cercaria is the same that I have utilized in all 

 my recent studies on larval trematodes. It is discussed in detail in 

 previous publications (Cort, 1917, pp. 49-50 and 1918a, pp. 129-130). 

 The snails intended for study were carefully opened and the viscera 

 removed, so that the dige.stive gland was as little crushed as possible. 

 If the snail were infected with the cercariae the digestive gland would 

 have a yellowish diseased appearance, since it would be literally riddled 

 with the sporocysts. Snails were opened early in the morning and 

 the cercariae which would be present in an infected host in large 

 numbers could be kept alive a whole day in ordinary tap water. 

 Therefore each infected snail found, gave material for a whole day's 

 intensive study of living cercariae. The cercariae, freed in a Syracuse 

 watch glass, were first studied with the lower powers of the microscope 

 to make an analysis of locomotion. Several cercariae were then trans- 

 ferred to a slide in a small drop of water and covered with a No. 1 

 cover glass. In order to slow down the movements sufficiently for 

 study it wa.s necessary to remove slowly the water from the preparation 

 with a piece of blotting paper until the cover glass pressed on the 

 living cercaria. The cercaria could then be studied until the drying 

 and pressure of the cover glass caused it to go to pieces. I usually 

 found it convenient to make a half dozen or more of these prepara- 

 tions at a time. A single day's study required the use of several 

 hundred preparations. The use of a compound binocular microscope 

 is indispensable for this type of work. The best results were obtained 



