STUDIES ON THE ËCTOPARASITIC TREMATODES OF JAPAX. 53 



Between these radial muscular fibres there are numerous nuclei, 



some of which are exactly similar to those of the general mesenchyma 

 of the body ; Ijut there are also others which are much larger and are 

 usually surrounded by a granular protoplasm (PL XI, figs. 1 and 2). 

 These I believe to be remnants of cells that have produced the muscular 

 fibres. 



The arrangement of the muscular fibres of the pharynx is in most 

 species as above described ; but there are numerous departures from 

 the rule. For instance, in Dididophom scssilis there are longitudinal 

 (or meridional) fibres on the ventral side, occupying a short strip 

 along the median line. In ^licrocotijle reticulata, again, the various 

 sets of mucular fibres and their arrano-ements are so anomalous that 

 they require separate description. They may be conveniently dis- 

 tinguished into the lojigitudinal, the circular, and the oblique fibres. 

 The circular fibres must again be divided into two groups, the internal 

 and the external. The internal circular fibres are situated next the 

 lining membrane of the pharynx at a short distance from it (PL IV^, 

 figs. 2 & o, int. c. ?».). They are most strongly developed a little 

 behind the middle of the length of the pharynx, and diminish towards 

 either end. They are divided into strong, compact bundles by the 

 radial fibres, which pass between them and are inserted into the lining 

 membrane of the pharynx. The external circular fibres are present 

 along nearly the whole length of the pharynx, but are especially 

 developed in its posterior half, and are there more numerous than the 

 inner fibres, -which they resemble in being divided into numerous, com- 

 pact bundles by the radial fibres. In the anterior half of the pharynx 

 they are less developed, and are divided into smaller bundles by the 

 oblique fibres to be presently described. In the lateral part of the 

 pharynx the external circular fibres are situated about midway be- 

 tween the inner and the outer limiting membrane of the pharynx ; 



