Cestode of the Genus Zscliokkeella. 41 



The lieacl (PI. VI. fig. 1) is rather wider than the neck, 

 its greatest width being O'OO mm. There is no rostellum, and 

 the most minute examination fails to reveal any armatm'e of 

 hooks, even on the suckers. The latter measure 0'17 mm. in 

 diameter ; they are sunk somewhat deeply in the sub.>tauces 

 of the head, and their orifices are flush with the surface. 



There is a considerable unseo-mented neck followins: the 

 head. Its width at first is only 0*43 mm., but on passing 

 backwards it becomes r^ipidly wider. Tlie segments are not 

 distinctly marked off from one another until a point is reached 

 about 3 mm. behind the head. The earliest segments so 

 marked ofl: measure 0'12 mm. in length and 0*8 mm. in 

 width. 



Throughout the strobila the segments are considerably 

 wnder than their length. The sexually mature segments 

 (Pi. YI. fig. 2) near the middle measure 0"-i7 mm. in length 

 and 3'5 mm. in width. Tlie measurements become much less 

 disproportional, however, in the gravid segments at the 

 posterior end, which are considerably narrower and at the 

 same time longer. 



The number of segments in an entire worm is about 230. 



The genital pores are unilateral, being situated in front of 

 the middle of each segment, near its anterior angle, and on 

 what appears to be the left side. 



Internal Anatomy. 



ParencJiyme and Musculature. — The cortical parenclij'me 

 is about equal in thickness to the medullary. It is denser 

 and more closely crowded with large nuclei. The muscles o£ 

 the body are not strongly developed ; there are, apparently, 

 no muscle-fibres lunning transversely or dorso-ventrally, and 

 the longitudinal fibres, though fairly numerous, do not form 

 a conspicuous layer in transverse section. 



JServous System. — The usual pair of lateral nerve-stems is 

 present ; they are rather stout and situated very near to the 

 outer border of the segments. Owing to the imperfect 

 preservation of the nervous system, I am unable to give a 

 fuller account of it. 



Excretory System. — The water- vascular system is very 

 interesting, and in some points seems to be unique. 



A distinct pair of doisal excretory vessels is present 

 throughout the strobila. These vessels are of very equal 

 calibre throughout, and do not appear to form any communi- 

 cation along their course, either with each other or with the 

 rest of the vascular system. They lie close to the dorsal 



