Development of Periphyllus testudo. 95 
In this state some of them were winged, others wingless. 
seqq.), L had already determined the species to be Aphis aceris 
(Linn.); and this was confirmed by the comparison of the 
winged individuals of the second generation with Kaltenbach’s 
and Koch’s descriptions of this species. 
After the nurses of the second generation had brought forth 
many young which perfectly agreed with the first life-phases 
of their mothers, I saw, in accordance with Balbiani's results, 
that individuals were born which I immediately recognized as 
Periphyllus testudo. The ordinary larvee were further deve- 
loped, and about the middle of May had become winged and 
wingless nurses, whilst the Periphylli had remained unaltered. 
e third generation, again, instheir turn gave birth at first 
to ordinary larve and afterwards to Periphylli, the latter even 
in greater number than had been produced by the second ge- 
neration. I was now much surprised by findmg among these 
larve examples which distinctly formed a transition between 
the two larval forms (the ordinary larve and the Periphylli), 
as in them the leaf-like appendages were fewer in number and 
more narrowly lanceolate, and, indeed, in some of them passed 
gradually into hairs. All these transitional forms were desti- 
tute of the regular figures which occur upon the back of the 
Periphylli, but possessed the two rows of setigerous tubercles 
and the two honey-tubes which we find on the dorsal surface 
of the ordinary larve, but which are wanting in the Periphylli. 
These mue ap became further developed, and, after the 
tion of the Periphylli of different generations. Up to the end 
of August I could not detect even the smallest change in 
them. At that time, however, they became thicker in the 
body, and on both sides of the back some darker contents 
