190 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



and unite with the caudal vesicle. The smaller, median frontal pair are the smaller 

 vessels described above for a shorter plerocercoid which becomes lost in the paren- 

 chyma around the end-organ forward and the caudal vesicle posteriorly, thus 

 exactly coinciding with Benedict's median frontal pair, excepting that this writer 

 did not see the posterior connections. The large size of this pair as desciibed 

 above for the 39 mm. larva must be due to some physiological condition or indi- 

 vidual variation since they are not thus distended in the 25 mm. specimens. An 

 important point to be noticed in connection with the development of the excretory 

 vessels is that the posterior end of the pleiocercoid remains in a primitive condition 

 while the anterior end specializes; and the development of the other parts bears 

 out this statement. 



The evidence given above appears to establish the idea of the identity of 

 this plerocercoid and P. ambloplitis, more especially with regard to the following 

 points : 



(1) The excretory vessels of advanced stages of the former are identical with 

 thos'^ of the latter; 



(2) Measurements of the cuticular structures and the parts of the suckers 

 are the same in both forms, relatively speaking; 



(3) The movements of the suckers during life are identical; 



(4) The nervous system of P. microperi is essentially the same as P. amblop- 

 litis; 



(5) The stages in the development of the end-organ, although not complete, 

 suggest a continuity between the two forms. 



The Intermediate Hosts. 



Our knowledge of the development of the genus Proteocephalus (Ichthyo- 

 taenia) dates as far back as 1878 (Gruber). Since then data have been added 

 from time to time, so that only now are we getting a general idea of the whole 

 process. Gruber found several stages of a plerocercoid in Cyclops breviciudatus, 

 which he believed to be those of Proteocephalus {Taenia) torulosa Batsch. 

 Zschokke ('84) found the unsegmented larva of P. longicollis JRud. in the liver of 

 Salmo umbla in which the adults were found, and what he called the larva of P. 

 torulosa, in Coregonvs fera in the month of January, in the intestine of Lota vul- 

 garis in the month of February, and in Alburnus lucidus in March. These ob- 

 servations in the light of present knowledge suggest a comparatively simple life- 

 history in that the larvae may develop from the oncospheres in the final host and 

 in a short period, as found by LaRue ('09). The former was also observed for 

 P. longicollis by von Linstow ('91). Riggenbach ('96) describes the plerocercoid 

 found in the parenchyma of the scolex of Corallobothrium lobosum Rigg., which 

 closely resembles that of P. ambloplitis found in the black bass and other fresh- 

 water fishes, but he gives no suggestions as to its adult existence. In the section, 

 rntitled, "Development," he merely mentions work contained in some of the above 

 eeferences, after saying that "on the development of the uterine eggs, as well as 



