Japanese TricJadida Marieola. 1 Q- 



Musculature. 



The dermal musculature presents nothing peculiar, and con- 

 sists, as is well known, typically of three sets of fibres, viz., the 

 circular, the transverse and the longitudinal. The outermost 

 circular muscles form a very fine layer directly beneath the base- 

 ment membrane, and appear in sagittal sections of the worms as 

 minute dots. In immediate contact internally with this there can 

 be recognised a delicate layer, in which the fibres are arranged in 

 two Ways, one runs from the right to the left backwardly, the 

 other from the left to the right backwardly. They cross per- 

 pendicularly with each other, and the fibres in the same ways are 

 nearly parallel to each other with some distance. It is very hard 

 to distinguish tliose fibres, though we are positiveh' al)le to 

 demonstrate them in horizontal sections. Inwards to the layer 

 there exists a layer of the longitudinal fibres, which is the most 

 developed of all the muscular layers of the body, and appears as- 

 sociated in distinct and quite regular bundles. Tlie fibres in 

 bundles extend from one end of the body to the other, without or 

 very rarely with anastomosing system, and are much more strong- 

 ly developed on the ventral than on the dorsal side. In the 

 species examined, the musculature of liJct. limnll is much better 

 developed than that of the others. 



In our forms the body muscles, also calling parenchyma 

 muscles, exactly coincide for the niost part with those of the 

 species studied by Böhmiq. As usual, several kinds of fibres can 

 be distinguished, viz., the dorso-ventral, the oblique dorso- and 

 ventro-lateral and the oblique longitudinal. Of these the dorso- 

 ventral muscles are very strongly developed in the species, with 

 which I have dealt. In the lateral portion of the body there are 

 also distributed two kinds of the oblique transverse muscles, 

 the first running dorso-laterally, the second ventro-laterall3\ 

 As stated by Böhmig, the oblique longitudinal fibres are pre- 

 sent, confined to the frontal part of the body, but the}^ are so 

 weakly developed that I have not been easily able to demonstrate 

 them. Besides, some fibres, regarded as the retractor or pro- 



