142 S- g<^tO. 



appearing only as a dark line in optic sections, and is closed towards 

 the base of the spines. In these species the spines either merely 

 rest on the lining membrane or are imbedded in the connective tissue. 

 In M. chiri the spines rest on the internal surface of the hemispherical 

 organ already referred to, and lie mostly imbedded in the mesenchy- 

 ma, with only their tips projecting into the genital atrium. 



Let us now turn our attention to the mass of connective tissue of 

 peculiar appearance so often referred to already, which is present in 

 many species around the genital atrium, and which extends in some 

 species for a certain distance around the vas deferens. 



In Microcotyle caudata (PL Y, fig. 3) .and 3Lfiisiformis(P].Y, 

 fig. 1) the mesenchyma on the antero-dorsal side of the genital atrium 

 presents an unusual appearance, and consists of compact, fibrous con- 

 nective tissue wholly destitute of nuclei, although these are very nu- 

 merous around ifc in M. caudata. In M. fusiformis this mass of connect- 

 ive tissue is of spherical form, and seems but little different front the 

 tissue around, the difference lying mainly in its greater compactness; 

 but in M. caudata its meshes are filled with a refractive, granular 

 substance, somewhat yellowish in the fresh state and more decidedly 

 yellow after treatment with borax-carmin. The granulation diminishes 

 towards the genital atrium, close to which it becomes exceedingly 

 fine. In M. elegms (PI. Y, fig. 2) and M. -sebastis (PI. VI, fig. 1) 

 there is a kidney-shaped mass of connective tissue wholly destitute 

 of nuclei, and very refractive — the refraction- being caused by 

 a perfectly homogeneous substance filling the meshes of the con- 

 nective tissue, the fibres of which are dii'ectly continuous with 

 those of the surrounding mesenchyma. In M. elegans there are some 

 coarse granulations close to the genital atrium at the place con-espond- 

 ing to the hilus of the kidney. In this species the kidiiey-ehaped 

 mass just described is pretty distinctly separated from the surrounding 



