1923 ] Occurrence, Life-Cycle, and Maintenance of Miastor 99 
Yellow larvae usually produce but a single embryo in the 
species {Miastor metraloas?) which I found in decaying wood. 
Yellow larvae (undescribed) occuring in mushrooms, however, 
produce a large number of embryos. I have frequently observed 
twenty embryos in a mother-larva. 
Neither the role of, nor the incentive factor producing, 
yellow forms is clear. 
In active yellow larvae I have observed a jumping locomotion. 
This seems to occur as a result of the larva bending its body 
until the anal chitinous hooks catch against the chitinous points 
of the second or third segment. Extension of the segments 
then tightens the tension which finally breaks with a snap re- 
sulting in a jump. The yellow forms are extremely active, and 
may often be seen lifting their heads and much of their bodies 
straight into the air. 
3) Pupa-larvoB. 
Larvae which will metamorphose into pupae are immedi- 
ately distinguishable from other forms by means of three char- 
acteristic differences, though in general their structure is similar 
to that of white and yellow paedogenetic forms. 
a) In newly born living pupa-larvae the imaginal discs are 
visible. These occur laterally in the third, fourth and fifth seg- 
ments. They are not present in paedogenetic forms. 
b) The spathula sternalis, a structure typical of Cecidomyid 
larvae, occurs ventrally in the third segment of the pupa-larvae of 
Miastor. It is not visible in newly born living pupa-larvae, but 
after four or five days becomes clearly visible, due to a yellow- 
ish coloration which later changes to orange and dark brown. 
The shape of this structure differs with various species. Its 
function is not understood. 
c) The eyes of pupa-larvae do not touch as in paedogenetic 
forms but are usually clearly separated. 
The fat-bodies of pupa-larvae are extremely well developed. 
The larvae are active up to the time of pupation, unlike paedogene- 
tic larvae which of necessity become inactive with the progressive 
destruction of their muscles, due to the development of the 
embryos. 
