50 ILLINOIS BIOLOGICAL MONOGRAPHS [i2,!^ 



at different levels but constantly located in the median frontal plane, diverge 

 as they meet the ganglionic mass in passmg forward, and consequently oppo- 

 site the bulbs come to lie close to the subcuticula laterally (Fig. 65). About 

 0.2mm. from the tip of the scolex they are united by a very irregular but com- 

 paratively large transverse commissure, from which large trunks pass to tlie 

 neighboring bulbs both forward and backward. This commissure has a length 

 €r longitudinal diameter of about 0.10mm., while its maximum depth between 

 the lateral pairs of proboscides is about 40jLi. It gives off large branches 

 anteriad to the lateral walls of the bulbs and caudad to the central walls. In 

 the latter case a large branch leaves the median portion of the commissure, 

 which is incidentally freely pierced with excretory vessels on each surface, and 

 shortly divides into two, each supplying the central walls of one of the frontal 

 pairs of bulbs (Fig. 65). The anterior branches likewise arise in a common 

 trunk on each side, which is in reality the continuation of the lateral ganglionic 

 enlargements of the commissure, but they supply the outside walls of the lateral 

 pairs of bulbs. Imbedded in the commissure are numerous nuclei which, on 

 account of their larger size than the neighboring parenchymatous nuclei, are 

 probably ganglionic or nervous in their nature. Just behind the posterior ends 

 of the bulbs and extending from 0.8 to 0.9mm. farther backwards (Fig. 43) there 

 is a large mass of large nucleated cells which m transverse sections (Fig. 66) 

 is seen to occupy the whole of the medulla (and about the whole of the section) 

 excepting for the excretory vessels. These cells are roughly spherical in shape 

 and have a maximum diameter of 25/.t, their nuclei being 5^. On account of 

 their finely granular consistency and their taking the counterstain quite like 

 the anterior nervous commissure they were interpreted as being ganglionic 

 cells. And this view was supported on closer study by the discovery that they 

 are not only united laterally with the chief nerve strands (Fig. 66), which can 

 scarcely be distinguished from them at various levels, but with each other 

 thru a compUcated plexus of fine longitudinal strands which pass forward to- 

 wards the bulbs and form around their bases an almost solid mass of fibrils 

 (Fig. 43). From this mass large strands from 10 to 15^ in diameter pass into 

 the bases of the bulbs, one for each, and are distributed among the retractor 

 muscles of the proboscis which they evidently supply. In the youngest 

 primary strobilas but not in the older ones, this mass of fibrils at the bases of 

 the bulbs evidently connects forward by a few strands with the commissure. 



Just as the definitive form of the anterior and posterior ends of the excre- 

 tory system is explained by the separation of the secondary strobilas 

 and the subsequent grooving over of the ends, so is that of the nervous 

 system, particularly anteriorly. As was noted by the writer (1914a) in cormec- 

 tion with the preparation of the original description of this species and shown 

 i n figure 11, the nerve-ring is drawn out anteriorly into a point which is directly 

 opposite a small conical pit in the tip of the scolex. This fact, as well as the 

 relatively small size of the nerve-ring, is explained by the contraction of the 

 free end of the "scolex" after separation and the growing together of the ends 

 of the nerve strands to form the ring. The close association of the nerve-ring 



