14 ILLINOIS BIOLOGICAL MONOGRAPHS [302 



suckers" as believed by Pintner (1880) to be the case in the Trypanorhyncha, 

 must remain mere suggestions for the present. Furthermore as to the forma- 

 tion of segments there are in Haplobothrimn not only conditions quite similar 

 to those in Bothriocephalus s. str. and other genera in which there is no neck, 

 segmentation begmning immediately behind the scolex, but those reminding 

 one of the proliferation of scoHces in echinococcus. In the former, as will be 

 seen below where the process is described more in detail (p. 102), a primary 

 segment divides up into secondary segments, these into tertiary segments, 

 and so on until there may be eventually thirty-two or more genital segments 

 corresponding to one primary segment formed immediately behind the scolex. 

 In Haplobothrium a primary strobila divides up into primary segments, these 

 subdivide into secondary segments, the definitive joints of the ordinary stro- 

 bila met with, which in turn may be subdivided again and evidently indefinitely 

 to form new chains. The chief difference between these two cases is one of 

 degree of regularity in the subdivision. Whereas in Bothriocephalus the whole 

 anterior region of the worm is affected, evidently no division taking place 

 after the rudiments of the reproductive organs have become separated from 

 the common rudiment, and the subsegments remain attached to one another, 

 in Haplobothrium not only do the primary segments separate as secondary 

 strobilas, but in the latter only a limited region is involved in further sub- 

 division. On the other hand there is somewhat of a resemblance between 

 this manner of subdivision in Haplobothrium and that of the larval Echinococ- 

 dfer in that the strobilas are developed from an original " nurse. " That is, 

 the primary strobila of the former might be looked upon as a nurse from which 

 are developed segments, comparable to the daughter-cysts of an echinococcus, 

 which in turn produce (secondary) scoHces and eventually strobilas. In other 

 words there might be recognized at first sight a sort of alternation of generations 

 in the case of Haplobothrium. But this comparison is only a superficial one, 

 for as will be shown below (under Haplobothriinae) the secondary scolex cannot 

 be considered to be a true scolex nor the secondary strobila a true strobila; 

 but the primary strobila with its four proboscides must be regarded as such. 

 Finally, this pecuhar method of segmentation reminds one of the asexual bud- 

 ding of some of the oHgochaete worms, particularly as regards the proliferation 

 of subsegments in the anterior region of the first formed divisions; but further 

 than this the comparison can scarcely be carried. 



