G Art. 4— S. Goto and H. Kikuchi : 



fibres. According to Wegener the diagonal fibres are absent in all 

 of the sixteen species of Dactylogyrus studied by him; the present 

 species seems to be an exception to the rule. The circular fibres 

 are exceedingly fine and are seen in longitudinal sections of the 

 worm as small dots lying in close contact with the basement 

 membrane of the cuticle. They appear to be better developed in 

 the middle part of the body in the region of the post-testicular 

 glands, where the fibres are thicker and more numerous. Around 

 the mouth the circular fibres are especially well developed and form 

 a sphincter. The diagonal fibres lie closely internal to the circular 

 and are thicker. The longitudinal fibres are best developed in the 

 caudal portion and are individually the thickest ones. They lie 

 internally to the diagonal fibres and are mostly separated from 

 them by intervening connective tissue. They are better de- 

 veloped on the ventral than on the dorsal side, and in the greater 

 part of the body run either singly or in bundles of a few fibres 

 each. In the caudal region the fibres are especially thick. In 

 some parts the longitudinal filtres are arranged in two layers, an 

 outer of isolated fibres and an inner consisting of bundles of a few 

 fibres each. Dorsoventral muscle fibres are fairly numerous in 

 some regions. 



As forming part of the system of longitudinal muscle fibres 

 must be regarded the retractor muscles of the pharynx and the 

 caudal disk. On the ventral side of the caudal region two or three 

 pairs of strong muscular bundles are very conspicuous in cross 

 sections of the body, lying more internally and separately from 

 the superficial fibres which form a practically continuous layer. 

 Shortly before the caudal disk these bundles subdivide and are 

 inserted to the hooks and cuticle. There are similar bundles also 

 on the dorsal side, but they are not so strong as those of the 

 ventral. A pair of fairly strong bundles of longitudinal fibres run 

 on either side of the median line in the middle part of the bod} 7 ; 

 posteriorly they become merged with the bundles of the caudal 

 region above mentioned, and anteriorly are attached to the 

 pharynx. 



The mouth is a small subcircular aperture on the ventral side 



