G2 



case in wliicli nucleated cells arise, except as the progeny of otlier cells. There is 

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

 namely, the colourless amceboid wandering lymph cells, whiph occur in the interstitial 

 lymph 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 membrane and so take up a position between that membrane and tlie surface 

 of the vitellii^e membrane, and then growing in size ft)rm the follicular epithelium. 

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

 decided ; Professor Emery in his monograph 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 raaturitj^ 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 

 Dvary, whence it passes out through the external genital aperture to the exterior, -vrhere 

 it is fertilised. 



The structure of the testis of the sole is very different from that of the ovary, and 

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

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

 a fuU-grojTi) 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 leading 

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

 of the organ. From the closed ends the tubes pass radially inwards towards the 

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

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

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

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

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

 communicate with a number of longitudinal tubes much smaller in nujnber than the 

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

 tubes. These longitudinal tubes convey the spermatozoa towards the efferent ducts, 

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

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

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

 the wall of the body cavity to which the testis is attached. Thus, to use the terms 

 frequently employed in human anatomy, the testis of the sole copsists of a cortical 

 portion and a central medulla, (he cortical portion consisting of tubes placed 



