62 



case in which nucleated cells arise, except as the progeny of other cells. Tliere is 

 thus only one source left to which we can attribute the origin of the follicular cells, 

 namely, the colourless aniccboid wandering lymph cells, which occur in the interstitial 

 l}nnph spaces of all connective tissue. These cells are usually small, and it is possible 

 that they might intrude themselves through the spaces between the fibres of the 

 follicular mem])rane and so take up a position between that membrane and the surface 

 of the vitelline meiubrane, and then growing in size form the follicular epithelium. 

 The question of the origin of the follicular cells cannot however be considered as 

 decided ; Professor Emery in his nionograph on Fierasfer, like myself, considers it 

 improbable that they are derived from the germinal epithelium, but expresses no 

 positive opinion as to their real origin. 



As the egg in the ovary increases in size and approaches maturity its circumference 

 reaches again the surface of the ovigerous lamella, and ultimately when it is quite ripe 

 the germinal epithelium, the follicular membrane, and the follicular epithelium burst and 

 the ripe egg enveloped only by the vitelline membrane escapes into the cavity of the 

 ovary, whence it passes out through the external genital aperture to the exterior, >vhere 

 it is fertilised. 



The structure of the testis of the sole is very different from that of the ov^ry, and 

 closely resembles that of the testis in other bony fishes. PI. XIII, 4, shows the structure 

 of the testis of a young male sole 9 in. long, killed February 4lh, 1889. The testis of 

 a full-grown male sole is similar, but I have represented the transverse section of 

 a small testis in order to include the whole of the section without making the 

 figure inconveniently large. The substance of the organ consists principally of 

 cylindrical tubes having walls of fibrous membrane and containing the spermatic cells. 

 These tubes are closed at the end which is most remote from the testicular duct leadins 

 to the exterior, and these closed ends are all situated immediately beneath the surface 

 of the organ. From the closed ends the tubes pass radialh^ inwards towards the 

 central region of the organ, except at the sides where their course is more longitudinal. 

 The tubes are sp numerous as to be in contact with one another along their sides. As 

 in the case of the ovary the " stroma " of the organ consists qf fibrous connective tissue 

 which fills up the interstices between the testicular tubes and forms a thin layer rouiul 

 the organ externally. In the central region of the organ the testicular tubes 

 conmuinicate with a number of longitudinal tubes much smaller in number than the 

 tubes themselves and of various sizes, some smaller, some larger, than the testicular 

 tubes. These longitudinal tubes convey the si)ermatozoa towards the efferent ducts, 

 and do not themselves produce spermatic cells : they are scattered with no regular 

 arrangement through the dense fibrous stroma. Infcriorly the fibrous stroma of the 

 testis is looser in texture and becomes contiiuious with the fibrous connective tissue of 

 the wall of the body cavity to M'hich the testis is attached. Thus, to use the terms 

 frequently employed in liuinan anatomy, the testis of the sole consists of a corlicid 

 portion and a central medulla, tlie cortical portion consisting of tubes placed 



