118 Mr. F. Walker's Descriptions 0/ Aphides. 



remained long in doubt upon this point. Ascribing this to the 

 minuteness of the insect, and the imperfection of my optical in- 

 struments, I sought for a rational solution, a physiological ex- 

 planation in the interpretation of an aquatic life, watched with 

 all care. I think I have succeeded in this ; I will state it in a 

 few words. In those active natatory evolutions, as also in those 

 brisk movements of the feet, when the insect is stationary, the 

 air combined in the water is doubtless disengaged from it by this 

 rapid beating ; and its invisible elements, constantly directed 

 toward the body by these centripetal impulsions, serve for a stig- 

 matic respiration. 



It is my intention to pursue the study of this phsenomenon 

 on some other insects, which, without branchiae, without down, 

 without fins, without oars, live nevertheless in the bosom of the 

 waters. 



XIII. — Descriptions of Aphides. By Francis Walker, F.L.S. 

 [Continued from p. 48.] 



96. Aphis Berberidis, Kaltenbach. 



Aphis Berberidis, Kalt. Mon. Pflan. 95. 70. 



This beautiful insect sometimes abounds on the leaves of the 

 cultivated barberry {Berberis vulgaris) from April till November, 

 and also occurs on other species of Berberis ; sixty or more of 

 them dwell under one leaf, the colour is changeable, and be- 

 comes darker and more various in the later periods of the insect's 

 yearly life, and especially in the egg- laying generation. 



The viviparous wingless female. This is hatched in the early 

 part of the spring, and is elliptical, rather flat, green, or pale 

 greenish yellow, or dull yellow, but is more often pale or bright 

 yellow ; it is rarely spotless, and the green colour which usually 

 adorns it appears first in a faint small spot on each side, where 

 there is often a row of bright green spots various in size and 

 in shape, and sometimes confluent, and forming a broken or 

 an entire line. These marks are most conspicuous during the 

 middle age ; they are hardly seen when the insect is very young, 

 and are almost lost in its full growth, and then it is also deprived 

 of the velvet-like skin which distinguished its youth, and becomes 

 more convex, shining and elliptical : the feelers are brown-yellow 

 at the base, and about half the length of the body ; sometimes 

 they are white with brown tips : the mouth is pale yellow with a 

 brown or a black tip : the nectaries are yellow or pale yellow, and 

 from one-fourth to one-sixth of the length of the body ; their 

 tips are brown : the legs are pale yellow ; the feet and the tips of 



