116 BULLETIN OF THE BUREAU OF FISHERIES. 



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There was also observed, in a considerable number of the more badly infested 

 fish, a cluster of cysts close behind the caudal border of the skull (fig. 1). Not all 

 the fish opened were examined for parasites in this position, but enough to make the 

 conclusion very probable that all badly infested fish have this cluster of cysts 

 behind the skull. None were found to occupy this position except in fish which 

 harbored large numbers of parasites, and they were found in all the badly infested 

 fish in which special search was made for them. 



If these cysts are present in the muscles of a fish they are easily found by 

 splitting the fish and removing the flesh from one side of the skeleton. If the fish 

 is badly infested it will be found to present some such appearance as that shown 

 in figure 1. When an infested fish has been opened in this manner, while many 

 cysts may be found in the muscle tissue which has been removed, a much larger 

 number will be found on the skeletal portion, where they lie in greatest numbers 

 between the vertebral spines. Masses of cysts completely filling the interspinous 

 spaces, especially on the ventral side of the vertebrae, were of common occurrence. 

 Some of these masses were as much as 5 and 10 millimeters in length and 3 and 4 

 millimeters thick. .Since an interspinous space is not far from 5 millimeters wide 

 it may be seen, allowing a cyst to occupy a space equivalent to a sphere 1 millimeter 

 in diameter, that from 120 to 400 cysts may be found in a single interspinous space. 

 This theoretical estimate was abundantly verified by calculations based on actual 

 count. Many of the badly infested fish also had numerous cysts lateral to the 

 centra of the vertebra?, especially in that part of the backbone lying dorsal to the 

 abdominal cavity. 



The cysts are easily recognized without the aid of a lens. Their outline is 

 usually short oval. Their color is in some cases a translucent bluish white, in others 

 ivory white, in others yellowish white. 



DETAILS OF EXAMINATIONS OF BUTTERFISH FOR CYSTS. 



August 8, 1904- — One. Cysts very numerous in the flesh. This specimen was 

 submitted to me by Dr. Lynd Jones, who stated that he had noticed these small 

 cysts in the flesh of butterfish which he had been feeding to terns, while he had seen 

 nothing of the kind in other fish which he had been cutting up for the same purpose. 



On the same date two other fish were examined. Cysts were found in large 

 numbers in each. While these cysts were somewhat variable in size, they did not 

 exceed 1 millimeter in length. Measurements of a typical one yielded the following 

 results in millimeters: Length 0.75, breadth 0.60; the blastocyst when liberated 

 front the cyst contracted and extended itself actively and varied from 0.4 to 0.7 

 in length; the larva, liberated from the blastocyst, also active, measured 0.67 in 

 length. 



August 18. — Six fish were examined for parasites in the muscle tissue and 

 were all found to be infested. Two had few parasites, one had many, and each of 

 the other three had enormous numbers. The cysts were oval and 0.8 by 0.7 milli- 

 meter in the two principal diameters. The favorite resting place of the cysts is 

 on the ventral side of the vertebral column, between and near the ventral spinous 

 processes. In the most highly parasitized fish the underside of the backbone from 

 a point opposite the insertion of the pectoral fin to the tail was thickly beset with 



