ON A NEW HISTBIOBDELLID. 305 



relatively, is remarkably firm, if one may judge from the 

 fact tliat the form of the body is not readily altered under 

 the action of various reagents. In Histriobdella this layer 

 is described hy Foettinger as structureless ; in Stratiodrilus, 

 on the other hand, it is marked by two systems of fine lines 

 crossing one another nearly at right angles, as in the cuticle 

 of many Chastopoda. The epidermis is a thin layer of proto- 

 plasm in which cell outlines are not recognisable, but in 

 which nuclei occur at wide and irregular intervals. No in- 

 tegumentary glands of any kind appear to occur with the 

 exception of those situated at the bases of the legs and of 

 the claspers, and a few small unicellular glands situated in 

 the neighbourhood of the genital opening in the male. 



The integument of Histriobdella would appear from Fcet- 

 tinger's description and figures to differ from that of Stratio- 

 drilus not only in the structureless character of the cuticle, 

 but in its relative thinness, and in the relative thickness of 

 the epidermis. 



The chief muscles of the body are the four longitudinal 

 muscles (figs. 1 and 9 — 13, in. d. and m.v.). These have the 

 form of thin flat bands, two dorsal and two ventral, extend- 

 ing from the neck constriction to the bases of the posterior 

 legs. There is no layer of circularly arranged fibres. The 

 fibres of these bands are flattened in a direction approxi- 

 mately at right angles to the surface of the body; each fibre, 

 of which there are only about ten to twenty in each bundle, 

 appears to extend through the whole length of the body. 



In front of the neck constriction, in the posterior part of 

 the head, the place of these longitudinal bundles is taken, to 

 some extent, by oblique and transverse fibres, by means of 

 which the movements of the head on the neck are effected, 

 by two pairs of retractor muscles of the jaws, and by the 

 retractors of the anterior legs. The transverse and oblique 

 fibres form an imperfect partition between the coelom of the 

 head and that of the trunk. 



In the third segment of the male are two pairs of retractor 

 muscles of the claspers (fig. 1, r. cl.) running obliquely out- 



