211] PROTEOCEPHALIDAE—LA RUE 211 



be twisted and pressed out of the regular position and spread far apart 

 by the granular mass. Radial muscle fibers showing the most typical 

 arrangement are to be seen in figure 45. Nuclei are plainly seen and 

 these are figured as the larger oval black spots. The drawing of the 

 endorgan (Fig. 43) is made from a head cut in a frontal or sagittal 

 plane. It shows the opening to the exterior, the basement membrane 

 and the cuticular lining of a part of this opening. It also shows the 

 cut ends of the muscle fibers next to the basement membrane. Some 

 of these same features may be well seen in other drawings (Figs. 45 

 and 46) which are drawn from transverse sections of other heads. 



It is evident from the structures here described and the drawings 

 which illustrate them that this organ is in reality a sucker. It is a 

 sucker which evidently comes to a certain state of development in which 

 as pointed out by the writer in his former paper on this species (La 

 Rue 1909:25), it is larger than the other suckers. The relative sizes 

 of this organ are shown in drawings reproduced (Figs. 27, 28) from 

 the former paper. This enlargement is due to a hypertrophy charac- 

 terized by the presence of granules. Altho the stages succeeding this 

 hypertrophy have not been followed out it is plain that the hypertrophy 

 is succeeded by an atrophy of the tissues. Since the granules are not 

 present in the adult organ they must disappear either as a result of 

 streaming out of the sucker opening before that is closed or they may 

 be absorbed by the organism. The sucker opening and the sucker cavity 

 and all traces of the cuticula, outer basement membrane, and muscles 

 about the sucker cavity are obliterated by the time this organ is found 

 in the adult cestode head. Thus the sucker loses all connection with 

 the exterior. It retains its limiting basement membrane, some of its 

 nuclei and perhaps a few scattered muscle fibers. The conclusion is 

 then that this endorgan, or muscle-plug as Johnston (1909 et seq.) has 

 called it, is a vestigial fifth sucker. That the writer was dealing with 

 the plerocercoids of this species is attested by the facts brought out by 

 his feeding experiments (La Rue 1909) in which he fed plerocercoids 

 taken from the flesh of Amblystoma to other uninfected Amblystoma 

 and the latter became heavily infected with the cestode Ophiotaenia 

 filaroides. 



The narrow neck is 3-4 mm. long. This is followed by a region of 

 short proglottids which gradually become longer and broader. The 

 increase in length is more rapid than the increase in breadth hence the 

 proglottids change progressively from broader than long to quadrate 

 and then to longer than broad. The youngest proglottids measure 0.30- 

 0.36 mm. broad by 0.10-0.17 mm. long. Ripe proglottids measure 1.6 

 mm. long by 0.8 mm. broad and in some cases as much as 4.0 mm. long 



