STUDIES OX THE ECTOPAEASITIC TREMATODES OF JAP AX. 31 



a very narrow, secondary zone of much refractive power and well 

 stained in haematoxylin. This zone is so narrow that it appears only 

 as a fine line, and its refractiveness and capacity of heing stained with 

 haematoxylin are much inferior to those of the primary zone. I have 

 observed some of these fibres bifurcatina: towards one of their ends 

 (PL XVir, figs. 7 and 12). 



The striped fibres above described are almost uniformly dis- 

 tributed in the secants into which the sucker is divided, as well as in 

 the radial elevations themselves. In the latter, the fibres lie at right 

 angles to their length,, - and are consequently very short (PI. XVII, 

 fig. 8). They may also be entirely absent from them for a more or 

 less wide extent (PL XVII, fig. 3). On the other hand, they are wholly 

 absent from those parts of the sucker which lie below the radial eleva- 

 tions. Here the substance of the sucker is entirely formed of connect- 

 ive tissue, the fibres of AA'hich unite into bundles on the ventral side 

 in such a way as to form a series of window-like cavities (PI. XVII, 

 fig. 3) ; while on the dorsal side the fibres form generally a compact 

 network, leaving only here and there a number of large cavities. The 

 centre of the sucker is wholly devoid of striped fibres, and is sharply 

 defined from the suri'ounding parts by a membrane of connective tissue 

 (PL XVII, figs. 4 and 5). This central part is traversed by the terminal 

 portions of some of the longitudinal fibres of the body, which are here 

 formed into bundles and ai-e inserted, some into the very centre of the 

 sucker, others more peripherally into the membrane of connective tissue 

 that separates the centre of the sucker from the surrounding parts. 



As may be inferred from the above description, the sucker of 

 Monocotyle is divided both externally and internally into eight equal 

 secants — externally by radial elevations, and internally by correspond- 

 ing radiating septa formed of fibrous connective tissue and wholly 

 destitute of striped muscular fibres. 



