102 ILLINOIS BIOLOGICAL MONOGRAPHS [102 



einer grossen Anzahl von Radialmuskelfasern besteht". Of this organ 

 in I. percae he writes, ' ' an der Spitze des Scolex findet sich das deutliche 

 Scheitel-organ, welches bei konservierten Exemplaren eine kugelformige 

 Anhaufung in der Langsaxe des Tieres gestrekter Zellen darstellt, die 

 ihren Charakter als Muskel-zellen offenbar vorloren haben. Wir sehen 

 hier ein rudimentares Organ, das, wie es scheint, jede Funktion einge- 

 biisst hat." The other differences in size and proportion of heads and 

 necks may be explained as being due to contraction states. The breadth 

 of the head when but a very few specimens can be measured is a valuable 

 tho not an absolutely reliable diagnostic character in a form which is so 

 variable and so contractile. In measuring Schneider's own specimens 

 the writer found the heads of the two forms very much alike. One head 

 of the I. percae was even smaller than the dimension recorded by 

 Schneider for I. ocellata, while every head of I. ocellata was broader than 

 the dimensions which he secured from measurements of the same form. 

 Their thickness in the writer's measurements was about equal to the 

 breadth as he recorded it. It is evident that size of head is not a valid 

 character for the differentiation of these two forms. 



As for the fifth sucker, examination of frontal sections of heads of 

 I. percae with an oil immersion lens revealed the true muscular structure 

 of a sucker. The drawing (Fig. 73) shows the nuclei, the radial muscles, 

 basement membrane, cut ends of circular muscle fibers, and the cuticula 

 covering the surface of the sucker. No cavity was noted in the fifth 

 sucker of either form. This last difference then between the two forms 

 vanishes. An examination of the two lots of Schneider's specimens 

 revealed a marked agreement in every diagnostic feature except in the 

 proportions of the proglottids and this slight difference was undoubtedly 

 due to different states of contraction. Most remarkable similarity was 

 found in the relations of the cirrus, cirrus-pouch, vas deferens, testes, 

 vagina, vaginal sphincter, uterus, vitellaria, eggs and position of the 

 genital pore. An examination of the comparative table and of the 

 drawings (Figs. 8, 73, 74, 69, 70) of preparations from Kraemer's I. 

 ocellata and drawings (Figs. 9, 71, 72) of his I. percae will at once show 

 the strong similarities. The differences which Schneider noted in the 

 shape of the ovary are readily explained as being due to contraction 

 states of the proglottid. Schneider's I. ocellata is clearly identical with 

 his 7. percae, and on account of the priority of the name suggested by 

 Miiller the latter should be retained. It should also be clearly recognized 

 that Taenia ocellata is a synonym of Taenia percae and hence can not be 

 used to designate any other species of cestodes in this genus. Schneider 

 then was not justified in using the name Taenia ocellata for the cestode 

 found in Coregonus lavaretus even had it proved to be a new species. 



