2^2 MR. J. T. CUNN'INGIIAM ON THIC [-^i"}' ^> 



EXPLANATION OF THE PLATES. 

 Plate XXYIII. 



Explanation of lettering : /, follicular epithelium ; v.m, vitelline membrane ; 

 z.r, zona radiata ; g.v, germinal vesicle ; b.v, blood-vessels ; c/.c, germinal 

 c?lls ; e, superficial germinal epithelium ; c, cells in interior of ovimi ; >/, 



yolk-masses. 



Fig. 1. Ovum of Lepidosiren (Protopferus) before commencing formation of 

 yolk. 



2. Ovum of Lcpidosircn (Protopteriis), to show the commencing formation 



of yolk. 



3. Ovum, with cells in interior. 



4. Nearly mature ovum, to shovr differentiation of yolk into a peripheral 



and central portion and modification of germinal vesicle. 



5. 6. Two ova, belonging to the same series as fig. 3, to show the proli- 



ferating follicular cells. 

 7. Early stage in development of ovum, represented in figs. 3, 5, 6, to 

 sliow the central mass of germinal cells which, at x, have com- 

 menced to fuse, and the invaginaled mass of cells which form the 

 follicular layer: o, immature ovum belonging to series represented 

 in figs. 1, 2, 4. 



PL.iTE xxrs. 



Fig. 1. Germinal vesicle of ovum (Plate XXVIII. fig. 4), more highly mag- 

 nified, to show its specialiaition into an outer and inner layer : 

 M, germinal spots. 



2. A portion of ovum (Plate XXVIII. fig. 1), more highly magnified. 



3. Germinal vesicle of same ovum, highly magnified, superficial view : 



«, germinal spots. 



4. The same, in section ; lettering as before. 



5. Portion of ovum a little more mature than that shown in Plate 



XXYIII. fig. 2. 



6. Nearly mature ovum. 



7. Less mature ovum of same series as last, to show the follicular epithe- 



lium resting directly upon the contents of the ovum; y, yolk- 

 particles in follicular cells. 



8. Very young ovum. 



9-20. Cells from interior of ovum (Plate XXVIII. fig. 3), showing 

 various conditions of division and degeneration : y' , yolk-particles 

 in interior of cell ; n, their nucleus ; y, yolk of ovum. 



3. On tlie Mode of Attachment of the Ovum of Osmerus 

 eperlanns. By J. T. Cunningham, B.A., F.R.S.E., 

 Fellow of University College, Oxford, and Superin- 

 tendent of the Scottish Marine Station. (Communicated 

 by Mr. F. E. Beddard.) 



[Eeceived April 20, 1886.] 



(Plate XXX.) 



Ill several works on Ichthyology and Pisciculture it is stated that 

 the ovum of the Smelt is adhesive. The mode of attachment is 

 described as differing from that which occurs in the Herring-ovum iu 

 the following manner : — In the Herring-ovum the whole of the outer 

 siiiface of the egg-membrane at the moment of deposition is gluti- 

 nous, and the ovum becomes attached at any part of tlie surface 



