*io""™lTpTri7«m] Roijal Microscopcal Societij. 179 



under description (Fig. 5), in whicli its position is most peculiar, — 

 the centre of the flat or attached side (Fig, 2). Here we find a 

 perforation in the ordinary shell-memhrane, having a diameter of 

 1-1 8 00th inch, and surrounded by an area of about 1-3 00 th inch 

 in diameter, which has somewhat of the funnel-Hke character 

 described by Dr. Kan some in the ovum of the Stickleback, and by 

 Professor Allen Thomson in that of the Salmonidee. I have not 

 been fortunate enough to obtain such a side view of this depression 

 as is represented by the latter author ; * but from the slightness of 

 the focal difference between its marginal and its central portion, I 

 should infer that the depression of the latter is much less in this 

 ovum than in that figured by Professor A. Thomson. Not impro- 

 bably, however, the form of this part may have undergone some 

 change during the process of embryonic development. 



Looking to the position of the Micropyle, and the closeness of 

 adhesion between the flat side of the Ovum and the subjacent sur- 

 face, I think it can scarcely be doubted that the fertilization of the 

 ovum by the entrance of the spermatozoa must have taken place 

 previously to its attachment to that surface. 



* Op. cit, fig. 68, B. 



EXPLANATION OF PLATE XLV. 



Fig. 1. — Upper or convex aspect of hemi-ellipsoidal Fish's Ovum, with contained 

 embryo. Magnified 40 diameters. 



„ 2. — Lower or flattened aspect of similar Ovum, from which the embryo had 

 escaped ; sliowing the Micropyle in its centre, and its entire surface 

 covered with filaments, whicli are longest at its margin. Magnifieil 

 40 diameters. 



,, 3. — Portion of this surface near the Micropyle; and Fig. 4, marginal portion 

 of the same surface, showing tlie relative length of the filamentous 

 processes in the two situations. Magnified 150 diameters. 



„ 5. — Micropyle, lying at the bottom of a shallow funnel-shaped depression. 

 Magnified 150 diameters. 



„ 6. — Section of a portion of the shell of Fusulina, showing the large perfora- 

 tions in its chamber-wall. Magnified 100 diameters. 



N 2 



