REPRODUCTION OP APHIDES. 113 



Unexpectedly, the males and the females were nearly 

 equally numerous in all the broods experimented upon. 



It may not be considered out of place here slightly 

 to remark on the ephippial eggs of Daphnia, which have 

 been at different times described by Dr. Baird, Sir J. 

 Lubbock, and others. 



Dr. Baird showed, as regard the water-flea, Daphnia 

 (which sometimes occurs in such quantity in our ponds 

 as to colour the water red), that a single copulation 

 is sufficient to fertilise the female through life ; and 

 Jurine thought that this fertilisation might extend even 

 through fifteen generations.* 



Two kind of ova are developed in Daphnia. 



The ordinary ova are transferred from the ovary into 

 a chamber near the back ; but the extraordinary ova 

 have their development in a kind of saddle attached 

 to the little crustacean, whence the term ephippial 

 ovum. 



They are also called by some authors hybernating 

 or winter eggs. From the impermeable integuments 

 which encase them, they can resist either a dry 

 heat or a considerable cold without loss of vitality. 

 As these eggs, however, are often formed during the 

 heat of summer, the term hybernating eggs, perhaps, 

 is not a very happy one. 



Von Siebold showed that these ephippial eggs 

 contain no germinal vesicle ; and Dr. Burnett main- 

 tained that they are instances of " internal gemmi- 

 parity," and just so he regarded the phenomenon of the 

 agamic reproduction of Aphis to be a process of 

 internal budding. 



Prof. Allman likewise agrees that these winter eggs, 

 which he styles statoblasts, are not true eggs ; but 

 separate granules, w T hich contain no germinal matter, 

 vesicle, nor macula ; and that they do not undergo 

 segmentation. Ephippial eggs, Dr. Allman says, may 

 even be budded from the stomach-walls of an animal. 

 Again, Prof. Huxley similarly shows a dissimilarity 



* W. Baird, ' Brit. Entomost.,' Bay Soc, 1849, p. 80. 

 VOL. IV. 8 



