184 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



bundle is about Z5n at its widest. This muscle-cross can be traced for 20 fi farther. 

 Just before it disappears its fibres become closely arranged in the centre of the 

 section, but the flared ends may pass a little farther back if any part of a sucker re- 

 mains past the decussation. From this and the appearances in longitudinal sections 

 passing through diagonally opposite suckers it is seen that the relation between 

 the end-organ and the muscle star is that of a body suspended in a sling; con- 

 traction of the fibres would obviously protract the apex of the scolex both by the 

 retraction of the suckers and the protrusion of the end-organ. 



Just before the posterior end of the end-organ is reached straggling fibres 

 coursing dorso-ventrally and laterally appear in four groups in the areas bounded 

 by adjacent suckers and the walls of the end-organ. Farther back these elongate 

 centrally and mingle with the descussation of the diagonal fibres before the latter 

 disappear (PI. XX, Fig. 10) the double crossing forming Riggenbach's "Muskel- 

 sterne". They are leather loosely arranged, are quite narrow as compared with 

 those of the diagonal gi'oup, and continue posteriorly to the caudal vesicle, around 

 which a few may be found; they are the dorso-ventral and lateral muscles of the 

 adult strobila (Fig. 12). Benedict in his paper on P. ambloplitis describes them as 

 originating from cells which may be situated anywhere within the longitudinal 

 muscles of the plerocercoid. The cell itself is spindle-shaped, has a large nucleus 

 which fills up most of the body of the cell and sends off fibres at least in two op- 

 posite directions. Other fibres crossing these muscle-cells near the centre give 

 the appearance of as many as four originating from one cell. The fibres themselves 

 run out into the cortical parenchyma well towards the absorptive cells. 



Longitudinal Muscles. — The longitudinal body-muscles are quite prominent 

 and situated about three-eighths of the length of the shorter radius from the cuticula, 

 (Pi. XXI, Fig. 12) ; towards the ends of the major axis of the more or less elliptical 

 cross-section they lie relatively nearer the latter. The fibres themselves cannot be 

 said to be regularly arranged in groups as described by Benedict for the adult, 

 yet here and there two to four and sometimes more are somewhat isolated from 

 their fellows. Towards the posterior end of the plerocercoid they approach the 

 centre, but at about the anterior end of the caudal vesicle they fall off considerably 

 in number. Anteriorly most of them after passing the neck constriction break 

 up into four groups each of which is attached to the posterior half of a sucker. 

 A very few fibres, however, pass by the suckers and become lost in the parenchy- 

 ma around the equatorial region of the end-organ. 



Parenchyma. — In the area enclosed by the longitudinal muscles the paren- 

 chyma is in the form of an open mesh-work of very fine fibres and cell-processes. 

 The nuclei of these cells are scattered irregularly throughout the area and are 

 easily confused with nuclei of dorso-ventral and lateral muscle fibres. The cortical 

 parenchyma, on the other hand, is more compact, the cells being arranged roughly 

 in a radial manner. Throughout the parenchyma, more especially in the medullary 

 portion, very many comparatively large spheroidal spaces are to be seen. These 

 may reach a diameter of 15/x. While the fixing of fresh material with glacial acetic 

 acid demonstrates the presence of much calcareous matter in the parenchyma by 

 effervescence and the passing out of gas^-bubbles through the cuticula, it cannot 



