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pleted, by examinations of the last brood or colony, during the 

 past two or three weeks of this autunan. 



My observations were made upon Aphis caryae (probably 

 Lachnus of lUiger, or Cinara of Curtis) one of the largest and 

 most favorable species for these investigations. This was in the 

 spring of 1853. The first colony, on their appearance from their 

 winter quarters, were of mature size, and contained, in their in- 

 terior, 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 

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

 primitive egg-like capsule ; at this time, I repeat, appear 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 Aphididse. These egg- 

 like bodies were either single nucleated cells of one three-thou- 

 sandth of an inch in diameter, or a small number of such cells 

 inclosed in a simple sac. These are the germs of the third gene- 

 ration or colony, and they mcrediSQ pari passu with the develop- 

 ment of the embryo in which they are formed, and this increase 

 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 

 appear like little oval bags of cells, — all the component cells 

 being of the same size and shape, — there being no one par- 

 ticular 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 



