313] PSEUDOPHYLLIDEA FROM PISHES— COOPER 25 



form aus Vogeln oft kleiner findet als die Larve aus Fischen, so mag das seinen 

 Grund datin haben, dass die letztere sich in der Grosse ihren Wirth anpasst; 

 die grossen Larven in grossen Fischen konnen aber nicht von kleineren Vogeln 

 verschlungen werden." The largest larval specimen at hand was one from 

 Catostomus commersonii which measured 425mm. in length by 15 in maximum 

 breadth, but the largest adult from Merganser merganser was only 217 by 6mm. 

 In the larva the anterior end is somewhat bluntly rounded (Fig, 1), the bothria 

 being \nsible as very short grooves passing over the tip, while in the adult they 

 are more elongated and distinct, the end of the strobila being somewhat pro- 

 truded as shown in figure 2 . On each surface of the larva there is a deep, median, 

 longitudinal furrow, which however, becomes obliterated in the adult, except- 

 ing anteriorly, by the growth of the reproductive organs, the ducts of which 

 are confined to the median line of the strobila. When these are developed 

 the strobila is characterized dorsally by a low median ridge bounded on each 

 side by a quite shallow groove, and ventrally by a greater thickening of the 

 median line, not separated, however, by any grooves from the lateral regions. 

 The whole strobUa gradually tapers from a short distance behind the anterior 

 end, where the maximum breadth is located, to the posterior end. Whereas 

 in the larva it is quite thick, in the adult it is thin and leaf-like, the margins 

 usually appearing wavy in alcoholic specimens, especially posteriorly. A 

 pseudosegmentation is present in the anterior end of the strobila, but as has 

 been known, especially since Liihe (1898) emphasized the fact, this division 

 of the strobila into segments does not correspond with the internal division 

 into true proglottides. Gemmill (1909:11) counted about 50 of them in the 

 anterior third of the worm, the writer 38 or 39 for a distance of 13mm. from 

 the tip of one adult specimen (Fig. 2) and 36 for 10mm. in another. They 

 vary considerably in length and are often incomplete medially. From the 

 anterior region showing external segmentation to the posterior end both larvae 

 and adults, but particularly the latter, are crossed by very numerous irregular 

 grooves, which give the worm its characteristic appearance apart from the 

 general shape as contrasted, for instance, with the closely related Schistocepha- 

 lus solidus. The smallest larva met with was one from a small specimen of 

 Micropterns dolomieu, 47mm. in length. It gave the following measurements: 

 length, 4.9mm.; maximum width, 0.54mm. ; width one-third the length from 

 the anterior end, 0.54mm., two-thirds, 0.37mm.; length of bothrial groove 

 about 0.07mm. 



The cuticula was found to have a thickness of from 5 to 15m, compared with 

 16 to 18/i by Kiessling and 2.1 (!) by Linstow. It appears homogeneous in 

 sections rather than divisible into the three layers described by the former, 

 with some tendency, however, for the outer one-quarter to one-sixth to take 

 the stain much less than the remainder of the tissue, which outer clearer area 

 is often bounded by a very delicate pseudociliated layer. There is a good deal 

 of variation not only in the thickness of the cuticula but also in its structure; 

 and these remarks apply to the larva as well as to the adult. The subcuticula 

 varies from 50 to 110^ in thickness, or 33 to 49/z according to Kiessling and 



