104 Proceedings of the Royal Society of Edinburgh. [Sess. 
Ecdysis. 
M. ribis has a large mortality in the first and second instars, and 
during observations on the moulting of sixteen individuals, only nine 
reached maturity. The aphides were frequently found dead in the first 
and second moults. Mr Brindley tells me that he has observed an appre- 
ciable mortality among cockroaches from entanglement with the tracheal 
tubes during ecdysis, and it is possible that this may hold for aphides also. 
This aphis, whether alate or apterous, like all others whose post- 
embryonic development is known, normally moults four times. The 
period of immaturity is variable and may be anything between six and 
nineteen days. 
Table K. 
Variation in the duration of the different instars. 
Date of Birth. 
Period 
between 
Birth and 
First 
Moult. 
Period 
between 
First 
and 
Second 
Moults. 
Period 
between 
Second 
and 
Third 
Moults. 
Period 
between 
Third 
and 
Fourth 
Moults. 
Period 
between 
Fourth 
and 
Fifth 
Moults. 
Period 
between 
last 
Moult 
and 
Birth of 
Young. 
Total 
Length 
of Imma- 
turity. 
June 22, 3 p.m. . . 
5 days + 
19 hours. 
4 days. 
3 days. 
2 days. 
5 days. 
19 + days. 
July 2, 6 p.m. . . . 
2 days + 
16 hours. 
1 day. 
2 
1 day. 
8 days. 
6 „ 
20+ „ 
June 9, noon (winged 
female). 
1 day + 
22 hours. 
4 days. 
3 
» 
3 days. 
12 „ 
May 29, 3.30 p.m. 
1 day + 
19 hours. 
3 „ 
2 
jj 
6 „ 
3 „ 
15+ „ 
June 21, 6.30 p.m. . 
15 hours. 
3 „ 
4 
1 day. 
1 day. 
10 „ 
June 9 
2 days. 
3 )5 
2 
55 
3 days. 
I 3 days. 
13 „ 
July 2, 3 p.m. . . . 
1 day + 
19 hours. 
1 day. 
1 day. 
1 day. 
1 day. 
5+ „ 
July 10 
2 days. 
2 days. 
4 days. 
4 days. 
4 „ 
16 „ 
July 11, 5 p.m. - . . 
Two moults 
in first 24 
hours. 
6 
55 
4 „ 
5 „ 
16 „ 
Averages 
2 days + 
4 hours. 
2 „ 
3 
2 „ 
... 
4 „ 
14+ „ 
Only one of the nine aphides included in Table K was winged, and she 
became mature in twelve days. Subsequent observations on the genera-, 
tion series showed that protracted development does not necessarily 
