204 Conservation Department 



The Second Intermediate Hosts. — Most of the experimental 

 work of the past season fell upon the fish which eat the animal 

 harboring the procercoid larvae of the tapeworm. Up to the sum- 

 mer of 1928 the only fish incriminated experimentally was the 

 large-mouthed black bass (A. salmoides). The experimental fish 

 were added to cultures of infected copepods and were left for 24 

 to 48 hours before examinations were started ; these were continued 

 at intervals. In this manner the rock bass {A. rupestris) was 

 infected in 80 per cent, the yellow perch {Perca flavescens) in 66.6 

 per cent, and the top minnow {FimdiUiis diaphanus) in 50 per 

 cent of the cases. Controls were of course examined in every case. 

 Fifteen young rock bass from the same lot used for the experi- 

 ments yielded no cestode parasites at all, while the 44 young yellow 

 perch gave only 4.5 per cent infection with P. amUopIitis, and 14 

 top minnows (Fundulus diaphanus) did not contain any tape- 

 worms at all. It is evident therefore that the figures secured 

 experimentally were significant. In most cases the parasites which 

 were recovered occurred encysted in the mesenteries of the host 

 (Fig. 11). In such locations a fibrous cyst is thrown about the 

 developing plerocercoid ; the cyst walls are less distinct in the 

 cases of the parasites recovered from the liver of the rock bass 

 and perch. Negative results were secured with the spot- 

 tailed minnow {Notrapis hiulsonius), the emerald minnow {N. 

 atherinoides) and the blunt-nosed minnow {Hyhorhynchus 

 not at us). 



In some cases infection was transferred from one host to the 

 other without any apparent change in the development of the 

 parasite. Thus infected liver containing young plerocercoids of 

 P. amhlopUtis were fed to 3 yearling small-mouthed black bass. 

 The same number of parasites which were fed were recovered a 

 few days later. Ten of these fish were examined as controls and 

 all were uninfected. In another experiment infected liver and 

 cysts attached to the mesentery were fed to the rock bass {A. 

 rupestris). The parasites were also recovered from these, some 

 from the digestive tract and some from the body cavity where 

 they had apparently re-encysted. No doubt re-encystment depends 

 upon the developmental stage attained by the parasite before inges- 

 tion takes place. Again upon two different occasions young pump- 

 kinseed sunfish (Eupomotis gihhosiis), 8 in all, which were can-y- 

 ing 100 per cent infection with the plerocercoids of P. amhlopJitis 

 were fed to as many yearling small-mouthed black bass {M. 

 dolomieu) . Some we kept for over tw^o weeks and when examined 

 50 per cent were infested. In this case all the parasites which were 

 found were recovered from the digestive tract. The plerocercoid 

 larvae were young and small (Fig. 12), and although the suckers 

 were usually invaginated they were thrust out from time to time. 

 Thei ones recovered at the end of the second week retained the 

 everted scalex (cf Fig. 13). 



It was found advisable to spend a portion of the time on the 

 shores of a pond which contained fish showing nearly 100 per cent 



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