STUDIES ON THE ECTOPAEASITIC TREMATODES OF JAPAN. 137 



deferens opens at the top of a papilla, which however is of the 

 shape of a truncated cone in this case, and projects into a cup-shaped 

 accessory cavity of the genital atrium. In some specimens I have 

 observed a layer of coarsely granular substance covering the in- 

 ternal surface of the vas deferens as well as the surface of the 

 truncate papilla, and of the cavity into which it projects; this is, in 

 my opinion, the secretory product of the prostate glands. In 

 M. chiri (PI. V, fig. 4) the genital atrium is very narrow and is 

 elongated in the dorso-ventral direction of the body, and the uterus 

 and vas deferens open into it close to each other. Its internal surface 

 is lined by an exceedingly thin membrane, and the spines, which are 

 vei'y similar to those already described as being present in the terminal 

 part of the vas deferens in M. raticulata, are in this species attached to 

 the internal face of a cup-shaped organ at the dorsal end of the atrium, 

 which will be described afterwards. In M. sciaence, again, the 

 genital atrium is an elongated cavity directed obliquely in an 

 antero-posterior direction and opening outwards by means of a very 

 small pore (PI. VI, fig. 2). The chitinous spines are of two forms, 

 the shorter and the longer, arranged in two circular sets around 

 the middle portion of the atrium; the shorter ones, which are hook- 

 shaped, being imbedded for the greater part of their lengths in the 

 substance of the wall of the cylindrical organ afterwards to be describ- 

 ed, with only their hooked ends projecting into the atrium. The 

 spines of th6 other set are much longer, and are slightly curved twice 

 in opposite directions; only their terminal parts project into the atrium, 

 and they are provided with a special set of muscular fibres, probably to 

 be regarded as belonging to the sets of dorso-ventral fibres which take 

 their origin from them and which, proceeding backwards and towards 

 the dorsum are inserted into the investing membrane on the dorsal side 

 of the body (PL VI, fig. 2). The uterus opens into the atrium near 



