140 ILLINOIS BIOLOGICAL MONOGRAPHS [428 



tudinal muscle layer proper, except that they are more scattered. ..." 

 Centrally the individual fibres of this group are of the same diameter as the 

 smallest of the main group, while peripherally they dwindle in size as they 

 approach the cuticula to such an extent that there they are indistinguishable 

 from the longitudinal cuticular fibres. Longitudinal sections show that they 

 bear the same relations to the salient posterior borders of the segments as are 

 described here for Clestobothrium crassiceps and other species and emphasized 

 by Liihe (1897a). Anteriorly a number of them pass off into the posterior 

 border in the typical manner ; but, as might be expected, they are comparatively 

 scarce in the posterior reaches of the strobila. Again, Linton stated that " the 

 longitudinal muscular fibres in general do not lie parallel with each other." 

 This was found to be more strictly applicable to those within the fasicles, since 

 only a comparatively few fibres pass from fasicle to fasicle longitudinally. 

 But, ^s in other species, they are continuous from segment to segment as are 

 indeed all of the groups of muscles, so that as far as their general arrangement 

 is concerned, Linton's (1890:731) statements are thoroughly justified: 



"Longitudinal sections were carried thru several contiguous segments. In 

 these there were no septa to indicate a division of the body into true segments. 

 The only indication of a segmented condition is the superficial character of 

 the projecting posterior edges. The longitudinal muscles are continuous and 

 the ovaries [uterus-sacs] are crowded together so as to form an almost un- 

 broken zig-zag line. So far as any internal characters go, the body is prac- 

 tically continuous." 



The musculature of the scolex is especially well developed, the sagittal 

 and radial fibres being very numerous. An unusual augmentation in the 

 number of the former appears towards the outside of the walls of the bothria, 

 extending from the dorsal to the ventral surface. Their exact course is ob- 

 scured somewhat laterally in the median frontal plane by the interdigitation 

 of the radial fibres which takes place there, that is, opposite the lateral grooves. 

 As the posterior borders of the scolex are approached they diminish in number 

 and size and eventually disappear. Coming into the base of the scolex as an 

 elliptical ring in cross-section with its thickness almost as much laterally as 

 dorsoventrally, the layer of main longitudinal muscles soon sends out dorso- 

 ventral horns into the walls of the bothria on each side and becomes arranged 

 in general much as in Clestobothrium crassiceps — doubtless an adaptation to 

 the almost closed nature of the bothria. The outer longitudinal fibres are 

 arranged on each side of the scolex as a continuous lateral band between the 

 lateral sagittal fibres just mentioned and the cuticula, and extending from the 

 dorsal to the ventral surface. Each bothriimi has a much smaller and thinner 

 band on each side next to the cuticula lining its cavity. The terminal disc is 

 almost completely filled up with very powerful longitudinal arcuate fibres for 

 the protrusion of its edges. 



In the anterior segments the two chief nerve strands are situated in the 

 medullary parenchyma between the lateral and median quarters of the trans- 

 verse diameter of the strobUa. From 18 to 30/i in diameter, they fill up the 



