465] PSEU DOPEY LLIDEA FROM FISHES— COOPER 177 



verwandeln. " Later Johnstone (1907:170) described the pseudoscolex with 

 considerable detail, finding quite the same conditions as did Linton. On ac- 

 count of never meeting with anything like a typical scolex in adult worms he 

 was led to conclude that "Probably in young codling, recently infected, a 

 stage of the cestode with such a scolex might be found but doubtless with in- 

 creasing age the changes mentioned above occur, and the normal structure 

 of the head disappears." And lastly, Scott (1909:85) made somewhat similar 

 statements, pointing out that " ... no satisfactory description of this part 

 of the v/orm [the pseudoscolex] has yet been pubhshed." Thus it is seen 

 that, apart from Olsson's (1867:54) finding in Gadus aeglifinus of a possible 

 young stage in the degeneration of the scolex of this species, no one has, as 

 yet, figured in detail its metamorphosis, Lonnberg, however, giving the only 

 description of the process. On the other hand, a typical scolex has been des- 

 cribed by several writers, as pointed out above, for what has been taken to be 

 the same species in Lota vulgaris^ but since there is evidence that the latter is 

 quite different from the species found in marine Gadidae and since the speci- 

 mens from Lota maculosa, studied by the writer, were found to belong to the 

 well known A. crassum, a pseudoscolex must be attributed only to adults of 

 A . rttgosum, at least until the confusion which exists in the literature regarding 

 the form from Lota can be cleared up by further investigation. 



Two forms of pseudoscolex which were dissected out by the writer from the 

 pyloric ceca of Melanogrammus aeglifinus, the haddock, and Gadus callarias, 

 the cod, are shown in figures 35, 36, respectively, the latter being from the 

 largest specimen at hand; while what is doubtless a younger stage in the 

 degeneration of the scolex is shown in figmre 34 from the intestine of a had- 

 dock. A series of transverse sections of the latter, brought out that the inter- 

 nal anatomy was quite suggestive of a typical scolex, that of A. crassum, for 

 example. As shown in the figure, the structure is somewhat flattened in the 

 dorsoventral direction. While there were only faint suggestions of bothria, 

 especially towards the tip, the arrangements of the muscles, nerves and ex- 

 cretory vessels pointed to its being possibly not far removed from the typical 

 form of scolex. This view is supported by the fact that it was found free in 

 the anterior part of the intestine of the haddock, altho, unfortunately, the 

 length of the strobila was not recorded. Among a lot of material taken from 

 several haddock two examples of the true scolex, as it would seem to be at or 

 about the time degeneration sets in, were found. The first one, shown in figure 

 32, was from the smallest strobila at hand, 22mm. in length, while the other, 

 figure 2)3, was from an older chain, only the anterior end of which was present 

 with a length of 32mm. and maximum breadth of 2.5. The second is evidently 

 the older from the standpoint of metamorphosis, since it is more conical 

 and less separated from the neck region which is slightly swollen; while the 

 bothria are disappearing as the whole structure is approaching the stage repre- 

 sented by figure 34. In figure 32 are seen somewhat more efficient bothria, 

 but the shape of the organ points to a considerable amount of degeneration 

 having already taken place. The next stage in the degeneration of the scolex 



