STUDIES ON THE ECTOPAEASITTC TREMATODES OF JAPAN. 15 



As may l)e seen fr<iin the figures referred to, the layer of 

 diao-onal fil)res is o-enerally separated hotli from tlie ch'cular and the 

 longitudinal fibres by a thin intervening layer of mesenchyma. 



Tlie layer of inner longitudinal fibres is the most strongly 

 developed of all the mnsculnr layers of the body, l)oth as a whole and 

 in the strength of the indi\'idu:d filtres that constitute it. In Axine 

 and in most species of MicyocotijJ(\ the fibres of this layer are not 

 arranged in liundles but are almost uniformly scattered in a distinct 

 layer of the mesenchyma (PL lY, figs. 6, 7, & 8 ; PI. A^III, fig. 1), 

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

 (PI. XXIII, fig. 7 & PI. XXIV, fig. 2), Onclweot>jh' (PI. XV, fig. 10 

 & PI. XVI, fig. N), and Hexacot>jIr (PI. XII, fig. o) the fibres are 

 united only into loose bundles ; l)ut in nearly all the other species stud- 

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

 and present in cross-sections generally polygonal outlines, evidently 

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

 Microcotiile irticulata, this inner layer of longitudinal fibres is again 

 divisible into two layers. In the f )rmer species the outer of the tv^o 

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

 distances from each other (PL XII, fig. 5). The longitudinal fibres 

 of Microcntijlc irticulata present some variations of arrangemerit, which 

 will be briefiy noted. 



In the more ;niterior ])arr of tlie body (PL V, tig. 0) the fibres 

 are in this species distributed apparently without order, but the 

 outer fil)res are considerably smaller than the deeper ones. In the 

 region of the vagina the fibres of the two lavers are -almost equal in 

 size (F^l. 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. 1). In this species 

 the circul:u- and diagonal fibres are but weakly developed and can not 



