PLANARIANS FROM MAURITIUS AND RODRIGUES 143 
Enclosed in the cup is a mass of visual rods, the outer extremity 
of which projects for a short distance beyond the margin of the 
pigment cup. Between the pigment cup and the mass of 
the visual rods, and also just in front of the outer surface of the 
rods, small spaces are visible, doubtless caused by shrinkage of 
the tissues. Each rod is an elongated, faintly staming, very 
finely granular body, which at the periphery shows a closer 
affinity for borax carmine than in the central part. In front of 
the opening is a collection of nervous matter, viz. granular 
substance and fibres surrounded by numerous cells, apparently 
belonging to nerve cells. The fibres pass over into the cavity of 
the pigment cup, but how the nerves stand in connexion with the 
visual rods I was unable to determine. 
Reproductive Organs (Pl. 4, figs. 7, 8)—The common 
genital aperture, lymg nearly mid-way between the mouth- 
opening and the posterior extremity of the body, leads into 
the wide, annularly outbulged vestibulum, which receives the 
opening of the penis-sheath from above. Both the vestibulum 
and the penis-sheath are lined with a single epithelium resting 
upon a fine basement membrane, beneath which are found 
circular and longitudinal muscular layers. Especially around 
the penis-sheath the muscular layer presents a thick, compact 
mass, which chiefly consists of circular fibres and is continuous 
with that of the penis. In the diaphragmatic part between 
both the cavities just mentioned the radial muscular fibres are 
present in a strongly developed condition. 
Male Organs.—Numerous follicular testes are placed close 
together in the ventral parts of the body, arranged in a single 
row on either side of the anterior main gut trunk, just on the 
dorso-lateral side of the longitudinal nerve cord. The row 
begins on each side slightly behind the ovary, and extends 
backwards nearly to the insertion of the pharynx. Each testis, 
of an oval shape, is made up of sperm-mother-cells and sperma- 
tozoa in all stages of development, surrounded by the tunica 
propria. In contact with the epithelium accumulations of the 
mother-cells occur, which contain very large, deeply staining, 
highly granular nuclei. In the cavity of the testis, and separated 
