14 S. GOTO. 



observed in some turbellarians. I have been able to demonstrate it in 

 all the three species of Diclidophara which I have studied. The 

 fibres are usually arranged in a single layer ; but on the ventral side 

 of Diclid. tetrodonis they are, irregularly, more than one layer thick 

 (PI, X, fig. 4). In the pedicels of the posterior suckers of the genus 

 under consideration, only the circular fibres are present (PL XII, fig. 

 4) ; the longitudinal fibres forming in each an axial bundle which is 

 attached to each sucker. 



The diagonal fibres that come next the circular, or in Diclidophora 

 next the outer layer of longitudinal fibres, are most strongly developed 

 in Tristomum. In Trist. ovale (PI. XXIIf, fig. 7 & PI. XXIV, fig. 2) 

 this layer consists of numerous fibres which are rather closely crowded 

 and cross each other at variable angles according to the different states 

 of contraction of the body. The individual fibres are somewhat 

 weaker than the circular- fibres. In Trist. sinuatum, on the other hand, 

 the absolute number of fibres that constitute this layer is considerably 

 less than in Tr. ovale, but the individual fibres are much stronger (PI. 

 XXI, fig. 4), and cross each other at an acuter angle. The last men- 

 tioned fact can not only be demonstrated by an examination of prepara- 

 tions in toto but is also evident from the fact that in sections of equal 

 thickness of the two species a shorter portion of each fibre is cut in the 

 one than in the other (c/. PI. XXI, fig. 4 & PI. XXIII, fig. 7). 



In Diclidophora the individual fibres of this layer are very much 

 finer than the longitudinal fibres, but are comparatively numerous 

 (PL XI, figs. 3 & 6 ; PL X, fig. 4). In Hexacotyle, on the other hand, 

 the fibres are not so numerous, but each one is only a little inferior in 

 size to the longitudinal fibre. In Axine (PL VIII, fig, 1) and Mono- 

 cotyle (PL XVIII, figs. 2 & 5) the fibres are very fine and not very 

 numerous. Finally in Microcotyle the diagonal fibres are very weakly 

 developed and can be demonstrated only in preparations in toto. 



