52 S. GOTO. 



eiFerent ducts of the numerous glandular cells presently to be 

 described. The internal cavity is in some species lined with a com- 

 paratively thick, structureless membrane of varying thickness, staining 

 well with haematoxylin, as in most species of Mtcrocottjle, Diclido- 

 phara (PI. XI, fig. 1), and Monocotyle (PI. XVIII, fig. 8) ; but in 

 others the lining membrane is. exactly similar to that which separates 

 the pharynx from the surrounding mesenchyma. The greater part of 

 the substance of the pharynx consists of mesenchymatous connective 

 tissue essentially similar to that of the other parts of the body and 

 traversed by numerous muscular fibres — the muscular fibres, how- 

 ever, predominating sometimes to an extraordinary degree and form- 

 ing almost the whole, as in Monocotyle (PI. XVIII, fig. 8) and 

 Microcotyle reticulata (PI. IV, figs. 2 and 3). 



The musculature of the pharynx consists typically of three sets of 

 fibres, viz. the internal and external circular fibres and the radial 

 fibres. In most species, the sets of circular fibres are arranged in a 

 single layer directly inside the limiting, membranes of the pharynx ; 

 but in some species they are more than one layer thick, as in Tristoimnn 

 sinuatum (PI, XXI, fig. 1) and Diclidophora sessilis (PI. XI,' fig. 1). 

 Moreover in all the species of Tristomum I have studied, these two 

 sets of circular fibres are developed in a special degree at the anterior 

 end of the pharynx, and constitute a powerful sphincter (PL XXI, 

 fig. 1 ; PI. XXIII, fig. 4 ; PI. XXIV, fig. 12 ; PI. XXV, fig. 7). 

 The radial fibres are but weakly developed in Microcotyle, Axine, Octo- 

 cotyle, and Oneliocotyle ; indeed, in the last-named genus I have not 

 been able to demonstrate their existence with enough certainty. 

 In Tristomum, Monocotyle, Diclidophora, and Microcotyle reticulata, how- 

 ever, they are more strongly developed. Like the dorso- ventral fibres 

 of the body, the radial fibres divide into smaller branches towards their 

 ends, and are inserted into the limiting membranes of the pharynx. 



