INTERNAL PARASITES OF THE SEBAGO SALMON. 1181 



ments on the activity manifested by these distomes, which climbed about on 

 the smelts and in them as they lay half digested in the stomach of the 

 salmon. 



This was so noticeable that I turned my attention at once to the smelt « to 

 ascertain if perchance it played any part in the life history of the distome. In 

 all, I have records of 52 smelts examined, and in 46 of these were found speci- 

 mens of Azygia sebago. The parasite occurred in the stomach only and the 

 infestation was small, from i to 14 distomes being found in each host, with an 

 average of only 4 to a fish. In most cases the parasites which were taken from 

 the stomach of the smelt were immature, not having yet reached that size at 

 which the production of ova begins; they were on the average 3 to 4 mm. long, 

 or in some cases even smaller, running from 1.5 to 2.5 mm. in length. Single 

 specimens reached a length of 6, 7, and even 10 mm. In one case, indeed, there 

 were none shorter than 6 mm., and the specimens varied from that to 10 mm., 

 so that one can not fairly maintain that they never reach the size attained in 

 the salmon. Nevertheless, after the account is cast up the average shows dis- 

 tinctly that the distomes do not reach their full size in the smelt and, so far as 

 collections made during July and August can indicate, those taken from this 

 host are usually small in size and sexually immature. I did not obtain any 

 information as to the source from which the smelt acquires its infection, but in 

 view of the universality with which smelt form the food of the salmon in Sebago 

 Lake the latter undoubtedly owe to them the major portion of their infestation 

 with this parasite. 



The host record of Azygia sebago is even yet unfinished. In the course of 

 my work numerous other fish from these same waters were examined. In 

 young specimens of Esox reticulatus 6 to 16 inches long I found this same para- 

 site reasonably abundant. To be sure, they seemed to average somewhat longer, 

 being 10 to 12 mm. in length in material from one host and 10 to 14 or even i& 



"This fish I am compelled to designate under the name Osmerus mordax (Mitchill), as Jordan and 

 Evermann (i8g6) do not recognize the Sebago smelt as a separate form, saying of the species "Atlantic 

 coast of the United States from Virginia northward to Gulf of St. Lawrence, entering streams and 

 often landlocked." Pam inclined to think that even in Sebago Lake there are two smelts. My atten- 

 tion was first directed to this possibility by Dr. W. C. Kendall, who, recalling our previous discussion 

 writes as follows in a recent letter: 



"You may recall that there seem to be two forms in the lake differing somewhat in size and habits. 

 The large form, which is the one that we caught with hook and line, is nearer to the marine smelt. 

 The small form is the one that we found in the salmons' stomachs. You will doubtless recall that the 

 principal food, when any at all was found in their stomachs, of the large form was small fish, generally 

 young smelts. Our examinations of the stomach contents of the small form show Entomostraca almost 

 exclusively. This difference is indicated also by the gillrakers, which are more numerous in the small 

 form." 



These distomes occurred equally in both sorts of smelt and those from the smaller smelts were 

 larger than those from the larger fish. This is, of course, a mere accident, but it serves to show that 

 the two types of smelt conduct themselves alike toward the parasite. 



