ANATOMY AND PHYSIOLOGY OF PATELLA VULGATA. 633 



noted. He has also described the olfactory organs, which lie in close relation 

 to the cteniclia. Fraisse's account of the eye of Patella ccerulea (Zeit. f. w. 

 Zool, xxxv. 461) agrees generally with that given above for P. vulgata ; the 

 chief difference seems to be that, in Patella vulgata, the " cuticularsaum " is 

 double. In both species the outer surface of the cuticle is provided with a 

 number of cilia — the " Faserchen " of Fraisse. Lacaze Dutiiiers' investiga- 

 tions into the nature of the auditory organ (Arch. Zool. Exper. i.) will be 

 referred to subsequently. With reference to the sense of touch, Clark (loc. 

 cit.) mentions but does not describe the minute tentacles (or " cirrhi," as he 

 terms them) on the mantle edge. 



7. Reproductive System. — The male and ,female reproductive elements are 

 developed in separate individuals. The glands are single, and pour their con- 

 tents, when ripe, into the cavity of the right kidney, from which they escape 

 by the right renal papilla, together with the urinary excretions. 



Male. — The male generative gland is a wedge-shaped, yellowish mass, lying 

 on the floor of the visceral cavity, and having its thicker side towards the back 

 and left side of the visceral mass. It is covered by a delicate membrane com- 

 posed of fibres of connective tissue, covered by squamous epithelium. The 

 gland itself is a spongy mass, less dense towards the centre. Peripherally, it 

 is composed of a framework of connective tissue, which sends processes 

 inwards, between which trabecular, therefore, are formed a large number of 

 " nests " in which sperms are developed. The trabecular are covered by cubical 

 epithelium, many layers deep, the superficial layers of which become the future 

 sperms. The manner of their development and their general appearance is 

 extremely like that of mammalian sperms, as described by Klein (Atlas of 

 Histology). The cubical epithelium is composed of rounded or polygonal 

 cells, variable as to size, but usually considerably smaller than a human blood 

 corpuscle. The superficial cells are slightly pear-shaped, and are arranged in 

 tufts or mounds. Each cell contains a nucleus and many granules, but a cell 

 wall is not visible (PI. CLIII. fig. 77). 



The process of development seems to be the gradual formation of a slender 

 filament at the attached end of the cell (PI. CLIII. figs. 78, 79) when superficial 

 and in its pear-shaped condition ; probably at the expense of the protoplasm of 

 the cell, the nucleus becoming the head. The appearance of the cellular tuft at 

 what may be termed the second stage is that of a raspberry, with the individual 

 drupes separated slightly from each other. In the next stage the tuft assumes 

 the appearance of a sheaf of barley, the " heads " of the grain corresponding to 

 the heads of the sperms. The entire tuft meanwhile has been growing, so 

 that ultimately any portion of the gland examined shows a series of long strands 

 of fibre fringed and tufted with delicate plumes. 



If a single plume be next examined, under a higher power, it is discovered 



VOL. XXXII. PART III. 5 M 



