1899-1900.] Dr R Stewart MacDougall on Genus Pissodes. 321 
on such a perfect periodicity, but the opinion, for its truth, takes 
for granted a comparatively short life in the adult stage, with the 
eggs all laid about the same time, and a rate of larval feeding 
extremely regular. But this does not hold even of the Bos- 
trichidse, which are quoted as a good example of it. Again and 
again I have taken members of the same species of Bostrichidae at 
the same time, and yet in very different stages of development. 
It is true that the intervention of winter produces a certain 
periodicity, inasmuch as the last-appearing beetles of the previous 
year and the earliest-appearing in the spring will start egg-laying 
at the same time ; hut that mature beetles of the same species can 
issue and proceed to breed in any of the warmer months can no 
longer be doubted. Outside of the Bostrichidae, Yon Oppen (1) proved 
this in 1885 for Hylobius dbietis , the large pine weevil, and now 
my experiments have proved that for the Pissodes no longer can 
the preparing of catch-trees be limited to so-called swarm periods, 
but must be attended to all the year from March till October. 
Position of the Pissodes in the Insect World. 
Of the families into which the Rhyncophora or proboscis beetles 
are broken up, one is the Curculionidae, and to it the Pissodes 
belong. * 
The Curculionidse may be defined rounded or oval beetles, 
possessing a beak of varying length, and distinctly elbowed 
antennae ; the females do not enter bodily into the tree for the 
purpose of egg-laying like the Scolytidae, but lay their eggs on the 
tree externally (rarely), or in a hole bored from the outside 
(generally), or, it may be, lay them in the soil. 
This family contains a very large number of genera, many of 
which are very important from the economic standpoint. The 
harm may be done by the grubs, more rarely by the imago, and 
rarest of all by both. 
Among the forms with destructive grubs are Otiorhynchus, 
whose larvae, hatching from eggs laid in roots or in the ground in 
their neighbourhood, gnaw the external surface of these and cause 
decay ; our genus Pissodes • the grub of Cryptorhynchus lapathi , so 
YOL. XXIII. 
X 
