202 Conservation Department f i 



to 48 hours. The first stage of this breakdown appears to be the 1 

 rupture of the granular secondary membrane liberating the larval 

 oncosphere and permitting it to wander about within the confines 



of the outer hyaline membrane. Soon thereafter the oncosphere j 



itself undergoes disintegration. j 



The First Intermediate Hosts. — As noted above the eggs of I 



the bass tapeworm must be eaten in a relatively short period of '' 



time. It was likewise suggested previously that the outer hyaline ^ 



membrane (which gives the egg its dumb-bell shape) must prove a ' 

 delicacy since it was observed that the Cyclops apparently trimmed 



it oif and usually rejected the inner membranes containing the ; 



oncosphere. Infection occurs when the embryo is accidentally | 



eaten with the membrane. During this summer eggs were re- i 



covered from the stomach of the Cyclops which had just been i 

 eaten. In this instance the rounded ends of the eggs had been 

 snipped off by the mandibles of the animal thus releasing the para- 

 site which was almost out of the shell as the secondary granular 



membrane had broken (Fig. 7). Whether this is the usual method 1 



of release of the parasite is a matter for conjecture. Normally the | 



oncospheres may be seen in the body cavity of the copepod four to \ 



five hours after ingestion. They undoubtedly reach their goal ! 



through the use of the three pairs of oncospheral hooks (Figs. 8,9). ! 



During the course of the experiments it was possible to infect i 

 only two species of copepods, Cyclops vulgaris ( = C. viridis) and 

 Eucyclops agilis ( = 6*. serndatus) (See Fig. 10). Negative results i 

 were secured with a cladoceran, Daphnia pulex, and Macrocy clops .| 

 anmdicornis (^C alhidus) . The successful infection yielded 50 and | 

 25 per cent respectively. Bangham^ reported finding the larval form ' 

 of this parasite in the body cavity of the well known Malacostracan, 

 Hyalella knickerhockeri. In 1928- he rei)orted finding a copepod 

 infected by the procercoid of P. amhloplitis. This he informed the \ 

 senior author had been identified as Cyclops Icuckarti; the senior 

 author gave Bangham credit for this in a recent publication know- i 

 ing that he had a paper in press. The paper however does not ; 

 mention the species of copepod. Infection of two other species , 

 experimentally was accomplished at the U. S. Fisheries Station in ; 

 Neosho, Missouri.^ These were C. prasinus and C. alhidus; the i 

 latter species of which is the same one {M. annuHcornis) with which ; 

 we secured negative results this past summer. For the experi- 

 mental work the following copepods were examined as controls ; I 

 C. vtdgai'is, 107 examined and 4.6 per cent infected; E. agilis, 121 ' 

 examined and 3.3 per cent infected, and M. annnlicornis, 75 

 examined and none infected. 



The following species have been experimentally infected, C. 

 prasinus, M. annul icornis, C. vulgaris and E. agilis. An unidenti- 

 fied species of copepod (previously denoted by Hunter as G. 



leuckarti) and H. knickcrhockeri are reported to act as the first ! 



intermediate host; these were determined by an examination of ; 



stomach contents. | 



', -, 'Loc. cit. I 



