A CESTODE PARASITE IN THE FLESH OF THE BUTTERFISH. 



115 



Cyst and blastocyst. — The walls of the cysts are comparatively thin, and in 

 sections are seen to be made up of a few concentric laj^ers of ci)nnective tissue. 



The plerocercus or blastocyst has a large number of comparatively coarse 

 calcareous bodies in the parenchyma; abundant contractile fibers occur in its wall, 

 whose outer layer is a dense cuticle. Each blastocyst contains a single scolex. 



The cysts lie both in the connective tissue septa and in the midst of the muscle 

 bundles. While the usual shape is oval, with longer diameter about 1 millimeter or 

 less, and the shorter diameter approximately two-thirds of the longer, a considerable 

 variety may be found where a large number of cysts is examined. For example, 

 among cysts removed from a lish in the lot from Barnegat, N. J., the following 

 dimensions, in millimeters, were recorded : 



In this lot the following additional measurements were made: Diameter of 

 proboscis, with hooks, 0.023; without hooks, 0.014; length of longer hooks, O.OOS. 

 Figures 12-16 show more variation in size and shape of hooks in different j^arts of 

 the proboscis than has lieen hitherto recorded for this species. 



DISTRIBUTION AND NUMBER OF CYSTS IN BUTTERFISH. 



The distribution of the cysts in the body of the fish is determined, in some 

 degree at least, by the position of the principal blood vessels. This is indicated 

 by the great uniformity which is maintained in the areas of infection. In all 

 cases where fish were found to be badly infested the greatest number of cysts 

 was found on the ventral side of the backbone, approximately halfway between 

 the abdominal cavity and the base of the caudal fin as in figure 1. While this 

 drawing was made from an actual dissection, it might well be a generalized sketch 

 or composite of all the more badly infested fish. 



There are in general four areas of greatest infection. Named in the order of 

 the greatest number of cysts in each they are: 



1. Below the backbone between the abdominal cavity and the caudal fin. 



2. Below the backbone and above the caudal third of the abdominal cavity. 



3. Above the backbone and opposite area 1. 



4. Above the backbone, opposite area 2, about halfway between the backbone 

 and the dorsal surface. 



