OF ARTS AND SCIENCES. 55 



Dr. W. I. Burnett read a memoir entitled " Researches on 

 the Development of the Aphides," of which the following is 

 an abstract : — 



" My observations were made upon Aphis carycB (probably Lachnus 

 of Illiger, or Cinara of Curtis), one of the largest and most favorable 

 species for these investigations. This was the spring of 1853. The 

 first colony, on their appearance from their winter quarters, were of 

 mature size, and contained, in their interior, the developing forms of 

 the second colony quite far advanced in formation. On this account 

 it was the embryology of the third series or colony that I was able to 

 first trace. A few days after the appearance of the first colony (A), 

 the second colony (B), still within the former, had reached two thirds 

 of their full embryonic size ; the arches of the segments had begun 

 to close on the dorsal surface, and the various appendages of the 

 embryo were becoming prominent ; the alimentary canal was more 

 or less completely formed, although distinct abdominal organs of any 

 kind belonging to the digestive system were not apparent. 



" At this time, and while the individuals B were not only in the ab- 

 domen of their parents A, but were also inclosed each in its primitive 

 egg-like capsule, — at this time, I repeat, appeared the first traces of 

 the germs of the third colony, C. Their first traces consisted of small 

 egg-like bodies, arranged two, three, or four in a row, and attached at 

 the locality where are situated the ovaries in the oviparous forms of 

 the AphididsB. These egg-like bodies were either single nucleated 

 cells of one three-thousandth of an inch in diameter, or a small num- 

 ber of such cells inclosed in a simple sac. These are the germs of 

 the third generation or colony, and they increase pari passu with the 

 development of the embryo in which they are formed, and this in- 

 crease of size takes place, not by the segmentation of the primitive 

 cells, but by the endogenous formation of new cells within the sac. 

 After this increase has continued for a certain time, these bodies ap- 

 pear like little oval bags of cells, — all the component cells being of 

 the same size and shape, — there being no one particular cell which 

 is larger and more prominent than the others, and which could be 

 comparable to a germinative vesicle. While these germs are thus 

 constituted, the formation of new ones is continually taking place. 

 This occurs by a kind of constriction process of the first germs ; one 

 of the ends of these last being pinched off, as it were, and so what 



