124 Proceedings of the Royal Physical Society. 
however, was obtained only from two districts—a limited number of adults 
and larve from Skene, Aberdeenshire, in October 1914, and the greater part 
from Darnhall, Peeblesshire, during 1915-16. 
Material used in Laboratory Observations. 
(a) H. ater material—Adults and larvee from Kingswells, Aberdeenshire, 
were the subject of experiments during winter, 1914-15. In October 1915, 
adults and larve were obtained from Drumshoreland, West Lothian, and 
Balerno, Midlothian. These, together with adults obtained at Balerno in 
April 1916, formed the material for the chief experiments. 
(0) H. palliatus material.—Adults obtained at Balerno, Midlothian, in 
May 1916, were used for laboratory experiments. 
Material for Field Observations. 
(a) H. ater material—The majority of the field observations on this 
species were made in an open Scots pine wood, near Balerno, in which a few 
trees had been felled, from the roots of which the laboratory material was 
obtained. This area afforded excellent opportunities for comparison between 
the life-history in the field and in the laboratory. Other localities were also 
visited, the chief being a felled area at Drumshoreland, Midlothian, and a 
receutly planted area on Darnhall Estate, Peeblesshire. 
(>) H. palltatus material—The chief centre for field observations on 
H. palliatus was a mixed wood of larch, spruce, and Scots pine near Balerno, 
Midlothian, which had suffered badly from snowbreak and windbreak.. It 
also afforded a check for the laboratory observations, as the laboratory material 
was obtained from it. Observations on H. palliatus were also made in other 
localities, the chief being a large area of Scots pine on Earlyvale Estate, 
Peeblesshire. 
(c) H. cunicularius material—Field observations on H. cunicularvus were 
restricted to two areas adjoining one another on Darnhall Estate, Peeblesshire. 
In October 1915, these consisted of a fairly extensive planted area and a 
smaller area in process of felling. In May and June 1916, this latter area 
was cleaned and planted, and on it all observations relating to the habits of 
HT. cunicularius were made. 
THE Structure oF H. ATER AND COMPARISON WITH H. PALLIATUS 
AND H. CUNICULARIUS. 
Methods. 
In the study of the structure of H. ater and comparison of it with that of 
its congeners, the following methods were adopted :— 
