Linton.— Seasonal Distribution of Parasites 55 



1907 June 7 6 No record of cysts in the flesh. 



iqm ? CP In 6 "Worms in flesh of each." 



1908 June 30 1 No record of cysts in flegh 



lono 2 i, 15 " Flesh ful1 of Parasites." 



o?n S OV ' S 6 " Man y c y sts ^ flesh." 



IS!? M ay l\ u " c y sts in flesh of 9." 



1911 May 22 12 "No worms." 



June 17 8 "No worms." 



Sept. 29 100 "Cysts in flesh of all." 



Uct - 3 100 "All contained cysts in flesh." 



So far as this record of Mr. Edwards's goes, it shows 

 a decided increase in the proportion of parasitized fish 

 in the latter part of the year. It must be remarked, how- 

 ever, that conclusions should not be drawn from occa- 

 sional examinations, even if considerable numbers of fish 

 are examined. This may be illustrated by a single case 

 compared with others of its class. It was noted in the 

 earlier years of observation of the flesh parasites of the 

 butterfish that the smaller fish, 100 millimeters or less in 

 length, seldom had parasites in the flesh. This continues 

 to be the rule. Thus, in 1912 out of 220 fish, measuring 

 less than 100 millimeters in length, that were examined 

 for flesh parasites, only 3 were found with cysts in the 

 flesh, and but few in either case. In 1914, out of 76 

 small fish examined but one was found with cysts in the 

 flesh, and in that case very few. In September, 1911, 

 however, I examined 270 small butterfish, under 100 milli- 

 meters in length, 12 on the 9th, 36 on the 11th, and 223 

 on the 15th, with the following wholly unexpected and 

 exceptional result : Cysts were found in each of the 270, 

 distributed as follows: 23 with very few cysts, 36 with 

 few, 78 with many, 66 with numerous, and 67 with very 

 numerous cysts in the flesh. In this case it is evident 

 that a school of small fish had been exposed to a common 

 source of infection at the same time. I think that there 

 can be no doubt that, as a rule, the butterfish that are 

 taken in the autumn, or late summer, in the waters of 

 the Woods Hole region show a larger percentage that 

 have cysts in the flesh than is the case earlier in the sea- 

 son. I have interpreted this as indicative of a general 

 northward movement of the butterfish from the warmer 



