STUDIES OX THE ECTOPAEASITIC TREMATODES OF JAPAN. 15 



As may be seen from the figures referred to, the layer of 

 diagonal fibres is generally separated both from the circular and the 

 longitudinal fibres by a thin intervening layer of mesenchyma. 



The layer of inner longitudinal fibres is the most strongly 

 developed of all the muscular layers of the body, both as a whole and 

 in the strength of the individual fibres that constitute it. In Axine 

 and in most species of Microcotijle, the fibres of this layer are not 

 arranged in bundles but are almost uniformly scattered in a distinct 

 layer of the mesenchyma (PI. IV, figs. 6, 7, & 8 ; PL VIII, fig. 1), 

 and present oval or circular outlines in cross-sections. In Tristomum 

 (PI. XXIII, fig. 7 & PI. XXIV, fig. 2), Onchocotyle (PI. XV, fig. 10 

 & PI. XVI, fig. 8), and Hexacotyle (PI. XII, fig. 5) the fibres are 

 united only into loose bundles ; but in nearly all the other species stud- 

 ied by me, the fibres of this layer are associated in compact bundles, 

 and present in cross-sections generally polygonal outlines, evidently 

 due to mutual pressure. In some species, as in Hexacotyle acuta and 

 Mici'ocotyle reticulata, this inner layer of longitudinal fibres is again 

 divisible into two layers. In the former species the outer of the two 

 layers is constituted by a single layer of strong fibres at various 

 distances fi-om each other (PL XII, fig. 5). The longitudinal fibres 

 of Microcotijle reticulata present some variations of arrangement, which 

 will be briefly noted. 



In the more anterior part of the body (PL V, fig. 6) the fibres 

 are in this species distributed apparently without order, but the 

 outer fibres are considerably smaller than the deeper ones. In the 

 region of the vagina the fibres of the two layers are almost equal in 

 size (PL V, fig. 5) ; but in most portions of the body the longitudinal 

 fibres are arranged in compact bundles, the outer fibres of which are 

 considerably smaller than the inner (PL III, fig. 4). In this species 

 the circular and diagonal fibres are but weakly developed and can not 



