ENEMIES OF APHIDES. 43 



It is exceedingly difificult to observe in a satisfactory manner 

 the earlier changes which take place within the eggs of Chrysopa. 

 At an early stage, when the egg is broken under the microscope by 

 pressure, the formation of nucleated cells may be seen to have 

 commenced, and the first observation I have been able to make is 

 the initial development of these for the formation of a blastoderm. 

 Brandt describes the structure at this stage of a blastodermic 

 envelope with some minuteness, and it appears to be identical 

 with that of Chrysopa. Prior to this, round or ovoid nucleated 

 cells are present in abundance, especially towards the lower end 

 of the egg, and it seems, as might be expected, the formation 

 proceeds by the subdivision of one or two of these cells, which 

 are of a different character to the remainder. The primary ger- 

 minative band floats rather freely on the surface of the yolk-mass. 

 This is much as Brandt describes in Calepteryx, and to my own 

 observation the development at this stage appears to be identical, 

 and to differ considerably from the development in some eggs 

 which I have examined, in which the band appears to be folded 

 within the yolk-mass. Later, the band may be observed to turn 

 inwards, as if about to penetrate the yolk. 



After the formation of the blastoderm a change takes place by 

 the separation of a layer, which seems to be the first indication of 

 the formation of the viscera, and here the resemblance to Calep- 

 teryx is again manifest. But in the latter, at an early point, the 

 germ so changes its position within the egg that the ultimate 

 position of the head of the larva is remote from that originally 

 occupied. It is not so in Chrysopa, in which the larval head 

 remains in proximity to the microphyle throughout the develop- 

 ment of the embryo. This important difference seems to me to 

 detract greatly from the value of the otherwise similar embryo- 

 logical growth. 



As the growth of the embryo proceeds, the extremity of the 

 abdomen becomes recurved so as to enfold the lower end of the 

 yolk-mass, and the head remains immediately below the micro- 

 phyle. The first development of limbs and cephalic appendages 

 is evident at an earlier stage, and during the remainder of the 

 growth of the embryo it follows precisely the progress of the 

 embryo of Calepteryx, as detailed and figured by Brandt. 



