128 ILLINOIS BIOLOGICAL MONOGRAPHS [416 



ruptedly into the base of the scolex as two narrow and very thick, dorso- 

 ventral bundles, somewhat trapezoidal in cross-section, and attach for the most 

 part as far forward as the terminal disc to the walls of the bothria in the usual 

 obHque manner. Only a very few pass on to the tip of the scolex. As might 

 be gathered from the prominence of the edges of the terminal disc, its longi- 

 tudinal arcuate fibres are also very well developed, and obviously essentially 

 related to the greater power of adhesion of the anterior part of the bothrium 

 on each face of the scolex. 



The nervous system consists of two chief strands, from 30 to 35/i in dia- 

 meter, passing thruout the strobila at the junctions of the lateral three-four- 

 teenths with the median four-sevenths of its transverse diameter. These 

 proportions are, however, in other parts of the strobila (especially anteriorly), 

 or in different strobilae, depending on the degree of contraction, often more 

 nearly 1:3:1. They are moreover usually nearer the dorsal surface of the 

 medulla than the ventral. This is on account of the fact that their course 

 is much interfered with by the testes, both having only a limited space 

 in which to accommodate themselves. They pass into the scolex close to- 

 gether — their axes actually about 70/i apart — and then very gradually diverge, 

 only to start to converge again about two-fifths of the length of the scolex from 

 its tip. After diminishing very sUghtly in diameter each enlarges into an 

 anteriorly truncated ganglion, united with its fellow of the other side by a 

 single commissure which is bent slightly forward into the tip of the terminal 

 disc. The anterolateral edges of the ganglia are at once split into two com- 

 paratively large nerves which pass out directly to the edges of the disc and at 

 right angles to the longitudinal axes of the chief strands. This arrangement 

 gives these anterior connections of the nerve strands a very characteristic 

 appearance both in transverse and frontal sections. 



The main longitudinal channels of the excretory system are at least four 

 in nmnber, only two of which, however, are at all constant in course, if not in 

 size. These occupy a ventral position thruout the strobila, while the remaining^ 

 vessels, two or more in number and connected by numerous and irregular 

 branches, are more dorsal in position. In the foremost segments the ventral 

 vessels are comparatively close together and situated considerably within the 

 nerve strands, i.e., towards the median line (Fig. 69). There they vary from 

 13 to 15)Li in diameter, the dorsal vessels having diameters as much as 18/z. 

 As all of these main vessels pass backwards in the strobila they diverge con- 

 siderably, and become more and more irregular in course as the reproductive 

 rudiments are neared. The ventral vessels, however, remain more constant 

 in course. In the anterior part of the proglottis they pass just outside of the 

 vas deferens on one side and the uterine duct on the other, while in the posterior 

 region of the genital segment they skirt the edges of the ovary or in many cases 

 pass beneath them. They may attain a diameter of 40/i. Furthermore, while 

 the dorsal vessels are forming a very open plexus by numerous large transverse 

 connections in the lateral portions of the medulla, the ventral pair give off at 

 right angles to their courses many short lateral branches passing among the 



