Mr. H. Seeley on some new Genera of Fossil Birds. 109 



ovum, a rounded mass composed of a group of small, pale, and 

 scarcely visible cells, enclosed in a common envelope, which 

 become more and more apparent in proportion as the egg ap- 

 proaches the term of its maturity. At this moment it is impos- 

 sible not to recognize in these elements the analogues of the 

 spermatic cells of which I have described the mode of formation 

 in speaking of the development of the viviparous Aphides. 

 These cells, indeed, present all the characters, even to the green 

 coloration due to numerous small pigment-granules, which I 

 have indicated in the latter ; and we may also recognize in them 

 even the little daughter cells in which the seminal corpuscles 

 will afterwards be developed. These facts evidently indicate 

 that the egg has already, while in the ovary, undergone a first 

 fecundation, with which the male has nothing to do, and the 

 eflfect of which is limited to the production of the generative 

 elements of the future animal. Now the agents of this fecunda- 

 tion are nothing but the seminal corpuscles developed in the 

 hermaphrodite apparatus of the embryo, and which are trans- 

 mitted by the latter to the adult female. 



After fecundation by the male, and the deposition of the egg 

 which succeeds this, the embryogenic work, properly so-called, 

 commences. The blastoderm appears in the form of a continuous 

 layer of cells surrounding the whole surface of the egg. This 

 blastoderm opens widely at its posterior part, and the mass of 

 spermatic cells penetrates towards the middle of the vitellus. A 

 wide canal, which extends from the posterior pole to the centre 

 of the egg, marks this passage for some time ; then the orifice of 

 the blastoderm closes, and the walls of the canal are effaced. 

 But, unfortunately, the egg, which, while these phenomena are 

 taking place, has acquired a darker tint at its anterior pole, due 

 to the coloration of the chorion, soon becomes covered from one 

 end to the other by a blackish veil, which conceals from the 

 observer the further phenomena taking place in its interior. 



XIX. — Note on some new Genera of Fossil Birds in the Wood- 

 wardian Museum. By H. Seeley, Esq. 



TERTIARY BIRDS. 



Ptenomis. 



Sternal end of a right coracoid from the Lower Tertiary of 

 Hempstead, Isle of Wight. It has much the size and form 

 seen in the Mute Swan ; but the exterior angle is rounded and 

 thickened, as in Bubo. The bone is compressed; the sternal 

 articulation is convex. There is nothing to show whether the 



