334 Proceedings of Royal Society of Edinburgh. [sess. 
the intervening winter, might he expected to be a perfectly 
regular one), the old dispute as to the generation loses some of its 
significance ; it is nevertheless of importance to know how long 
individual development takes. 
What, then , is the period of time represented from the egg-laying 
through the larval and pupal stages and up to the issue of the 
individual imago ? 
I give in tabular form some of the results. 
Length of Time for Development . 
No. of 
Pine. 
Beetles placed 
on Pine. 
First Imagos 
Issue. 
Length of Time. 
1 
End of March 1896 
July 24, 1896 
114 to 120 days. 
2 
April 17, 1896 
Aug. 24, 1896 
128 days. 
3 
June 17, 1896 
Oct. 15, 1896 
119 „ 
12 
April 15, 1897 
Aug. 31, 1897 
137 „ 
14 
April 21, 1897 
Sept. 8, 1897 
139 „ 
16 
May 10, 1897 
Sept. 24, 1897 
136 „ 
17 
May 25, 1897 
Sept. 29, 1897 
127 „ 
19 
May 29, 1897 
Sept. 18, 1897 
111 „ 
20 
June 3, 1897 
Sept. 20, 1897 
108 „ 
In each case the time is reckoned from the day on which the 
beetles were placed on the plant. 
To take the general results given in the table, without com- 
parison of different weather conditions, the shortest period taken 
for development was three and a half months, and the longest, 
four and a half months, showing an average over nine cases, extend- 
ing from April to June, of four months. 
Yery different, however, is the result if the larva he overtaken 
by the winter, the period of the development extending then over 
ten or eleven months, e.g ., pine 3 held in November 1896 full- 
grown larvae in their beds, and these did not reach the imago stage 
till — the earliest on June 24th, and the last on June 27th, 1897, over 
ten months since this pine had been left free from beetles. This 
is further shown in the accompanying table : — 
