296 THE VOYAGE OF H.M.S. CHALLENGER. 



centrifugally, but these do not reach to the investing membrane. They are, moreover, 

 divided from it by a layer of cells and fibres 0'024 mm. in thickness. 

 ' There is a single layer of irregular cells with an average diameter of O'Ol mm. 

 (PI. LXXI. fig. 33, c) lying close to the inner surface of the membrane {b). Their 

 nuclei are conspicuous, spherical, and can be readUy stained. Between and over these 

 cells, which are divided by small intervals, fine fibres running in all directions (PI. LXXI. 

 fig. 33), are found together with numerous bloodvessels. These fibres extend up into 

 the partitions dividing the lower portions of the centrifugal parts of the gland-tubes 

 from each other. 



With a low power this layer of ceUs and fibres appears as a granular zone 

 (PI. LXXI. fig. 32). It corresponds to that of Chmdiodus sloanei figured by Ussow 

 (Joe. cit.) in fig. 7, pi. ii. Above the central space or lumen of the gland, 

 which is usually occupied by the granular non-transparent secretion, a disc, which 

 deserves particular attention, is situated, and occupies the whole of the constriction, 

 and in this way completely divides the contents of the spherical from those of the cup- 

 shaped part of the organ. It is 0'16 mm. broad, circular, expanded in a plane vertical 

 to the axis of the organ, and O'l mm. thick. The upper external surface is flat, whilst 

 the lower surface, looking towards the interior of the spherical part, appears slightly 

 convex and projecting in the centre into the lumen of the gland (PI. LXIX. 

 fig. 3). 



This disc is divided by a kind of diaphragm, which is not very distinct, into two 

 portions, an external and an internal. The diaphragm appears as a continuation 

 of the inner membrane, stretched out within the projecting ring of the incision which 

 divides the cup-shaped from the spherical portion of the organ. 



The whole of the disc is composed of large irregular cells, which readily become 

 stained and contain large spherical nuclei, 0"008 mm. in diameter, which then appear 

 exceedingly prominent. Although the contours of the cells are not very distinct, I have 

 been able to see them in the organs of all the specimens examined by me. 



This double disc of large cells is very conspicuous ; it corresponds, as far as its position 

 is concerned, with Ussow's' "lens." Leydig^ represents it as a portion of the granular 

 secretion occupying the lumen of the gland. 



The space above this disc — the cup — is filled with a somewhat granular substance in 

 which radial lines are very clearly visible with a low power (PL LXXII. fig. 32). A similar 

 radial structure has been observed in this part of the organ by Ussow ^ and Leydig* ; but 

 while the former .supposes it to be caused by irregular threads pervading the structureless 

 substance filling the cup, the latter sees in it the expression of radial gland-tubes 

 similar to those found in the lower spherical portion of the organ. 



• M. Ussow, loc. cit., pi. ii. i\<^. G k, I. " F. Leydig, top. cit., pi. vi. fig. 33. 



3 M. Ussow, loc. cit., pi. ii. fig. 6, x. * F. Leydig, loc. cit., pi. vi. fig. 33. 



