1914] A New Cestode from Amia Calva L. 93 



Nervous System. 



The nervous system consists of a nerve-ring situated immediately 

 beneath the tip of the scolex and covering the median excretory vesicle 

 (vide infra) Hke a cap, and the two chief strands passing back from it 

 through the whole of the strobila. The former is a comparatively 

 weakly developed structure (Fig. 11), elliptical in transverse section, 

 with diameters of 60 and /^Ojj.. The chief nerve strands are i8/i in dia- 

 meter in the scolex, in which they are situated between the middle and 

 lateral thirds of the medullary parenchyma (Fig. 34), while in the 

 anterior proglottides they are somewhat larger, excepting in the inter- 

 proglottidal region. Here they narrow down suddenly to a diameter of 

 8/x. In the posterior unsegmented portion of the strobila they are quite 

 flattened laterally, opposite the gravid uterine sacs (Fig. 19), on the whole 

 somewhat smaller than in the jointed region and situated in the medulla 

 but quite close to the longitudinal muscles (Fig. 18). The nerve-ring 

 gives off besides the two chief nerve strands, eight others, four being 

 grouped around each of the former (Figs. 34 and 35). It was at first 

 difficult to decide whether these were distinct strands or only the inter- 

 sections of an extensive meshwork of nerves situated in the cortical 

 parenchyma and thus comparable to the " plasmatische canal system" 

 of Sommer and Landois ('72) ; however, with further search eight strands 

 could be followed throughout the segmented portion of the strobila. 

 The difficulty in following them is due to the fact that the nervous 

 branches given off mostly centrally are quite as large as the strands 

 themselves and that they anastomose freely with one another and with 

 the chief strands which are, however, much more distinct. These colla- 

 teral nervous tracts gradually disappear with the appendages posteriorly. 

 Thus they are apparently developed in connection with the extra mus- 

 culature of the latter. Since the Golgi method of impregnation was not 

 used on any of the material for this study, the nerve-strands were seen 

 to be made up of only a very fine fibrillar meshwork containing extremely 

 minute granules and vacuoles. 



Excretory System. 



There are three excretory vessels coursing throughout the strobila, 

 a large median one evidently the morphological equivalent of the dorsal 

 pair of many Bothriocephalids and two much smaller, ventro-laterally 

 situated, all being located in the medullary parenchyma (" Markschicht") 

 between the chief nerve strands (Figs. 34, 35 and 37). Immediately 

 behind the nerve-ring the median vessel expands to form a somewhat 

 spherical vesicle from 25 to 40 ^ in diameter, into which the lateral 



