IdHti. 21 
vTorked out. As far as colouring is concerned, there seems to me some ground for 
the hypothesis that light is the chief agent, and that the chief time of its producing 
this effect is during the larva state. There is much ground from analogy for this 
belief, and some from actual fact. If we take Pontia rapce for example, we find that 
the autumn brood, i.e. those whose larvae are exposed to the greatest duration of 
sunlight, are the most abundantly supplied with pigment scales. For the same 
reason boreal varieties, where the larvae are summer feeding, are generally darker 
than more southern examples. We must bear in mind that light produces its effect 
in a twofold manner — by intensity and by duration. Now, in any animal whose 
life is for a year, as the actual quantity of daylight is equal all the world over, 
intensity alone is brought into play ; but this is not the case with a larva living 
only, perhaps, for one or two summer months. That the chief period in which this 
is caused is during the larva state I presume from the fact that shutting up pup» in 
dark boxes has no evident effect, and that many Noctuw (as X. lithoxylea for 
example), whose pupae are always excluded from light, are yet strongly subject to 
boreal variation. That rapidity of development in the pupa state does not produce 
the difference may be easily proved, as the chrysalides of F. rap(s, if kept in a very 
warm place and perfected, before Christmas even, are always of the light variety 
or Metra. It must be i-emembered that these thoughts are only given as a possible 
hypothesis which may lead to the working out of an unsolved problem by calling 
other experimenters into the field ; and it must be looked upon as very fortunate 
that such a corpus vile as Pontia rapoB is provided for all who wish to work at 
the subject. — R. C. R. Jordan. 
Occurrence of Stenus glacialis, Heer ; a species new to Britain. — My friend Mr. 
R. Hislop, of Falkirk, has sent to me for examination a specimen of a conspicuous 
Stenus, taken by himself on the 4th of last August, on the Cheviots ; and which I 
am inclined, from the preponderance of characters wherein it agrees with the 
published description of that insect, to refer to the S. glacialis of Heer (Faun. Col. 
Helv., P. I, fasc. 2, 224, 35 ; Kraatz, Ins. Deutschl., ii., 787, 58). On account of its 
size, colour, general appearance, and build, — and especially its very slender legs 
and antennae, — Mr. Hislop' s insect is primo visxi strongly suggestive of S. lustraior, 
and its allies with simple tarsi ; but a close examination reveals the narrow and 
small bilobation of the fourth joint of its slender tarsi. It is black, slightly metallic, 
shining, sparingly and very strongly punctured ; with thin long pubescence, and 
testaceous palpi and legs, the femora (especially of the middle and hinder pair) 
being broadly fuscous at the apex. The head is wide, with prominent eyes, and 
very long and slender antennae, dark at the apex, and set with fine hairs, — the 
3rd joint being twice as long as the 4th. The thorax is somewhat strongly con- 
tracted behind, with a fore-and-aft abbreviated longitudinal furrow, and other slight 
irregularities ; the elytra are rather depressed at the suture, and about one-third 
longer than the thorax ; and the punctuation of the abdomen, though deep and 
strong for the most part, nearly vanishes towards the apex. 
The long pubescence, especially pointed out by Kraatz as an efficient diagnostic 
for this species, is not conspicuous in all parts of Mr. Hislop's specimen, which is 
rather abraded ; but, towards the sides of the elytra, and elsewhere, it is very 
evident. 
