JO 
NADRORE 
| NOVEMBER 15, 1906 
taken this year.—G. J. Porritt: A series of Abraxas 
grossulariata, var. varleyata, bred this year from a pairing 
of the variety, all the brood being of the variety: none 
showing the least tendency to revert to the ordinary form. 
—C. P. Pickett: A gynandromorphous specimen of 
Angerona prunaria bred by him, and a ¢ specimen of 
Fidonia atomaria, caught at Folkestone, with six wings. 
—F. W. and H. Campion: Specimens of the rare 
dragon-fly Sympetrum flaveolum, taken near Epping 
in August last. It was suggested that these were 
part of a migration of the species such as occasionally 
takes place.—Dr. F. A. Dixey: Specimens of Nychitona 
medusa, Cram., Pseudopontia paradoxa, Feld., Terias 
senegalensis, Boisd., Leuceronia pharis, Boisd., and 
L. argia, Fabr. Although there does not exist any direct 
evidence that the members of the genus Nychitona are 
distasteful, their habits are such as to suggest this mode 
of protection, and there is little doubt that they have served 
as models for other insects.—H. St. J. Donisthorpe : 
Examples of Dinarda pygmaca, Wasm., with our other 
three species, D. hagensi, Wasm., D. dentata, Gr., and 
D. méarkeli, Kies., with their respective hosts.—Dr. N. 
Joy: Species of Coleoptera first recognised as British in 
1906; a variety of Lathrobium elongatum, L., from South 
Devon, with entirely black elytra, and which he proposed to 
eall var. nigrum; a curious dull aberration of Apteropeda 
globosa, Ill.; Heterothops nigra, Kr., taken in moles’ 
nests; and a species of Gnathoncus differing in certain 
characters from G. rotundatus, Kugel, and which occurs 
almost exclusively in birds’ nests.—G. B. Oliver: A 
melanic @Q of Acidalia marginepunctata, Goeze, and a 
melanic ¢ of A. subsericeata, Haw., both taken in North 
Cornwall this summer, together with the typical forms for 
comparison ; also a dark aberration of Coenonympha pam- 
philus, Linn., taken in the same district.—President: A 
series of Selenia bilunaria, illustrating the remarkable 
angulation of the wings in these examples.—Papers.—The 
formation of a new nest by Lasius niger, the common black 
ant: H. W. Southcombe.—Some notes on the dominant 
Miillerian group of butterflies from the Potaro River district 
of British Guiana: W. J. Kaye.—A contribution to the 
classification of the coleopterous family Passalide: G. J. 
Arrow. 
October 17.—Mr. F. Merrifield, president, in the 
chair.—Exhibitions.—H. St. J. Donisthorpe: Living 
specimens of the beetle Mononychus pseudacori found 
in plants of Iris  foetidissima found at Niton, 
Isle of Wight.—A. H. Jones: A collection of butterflies 
from Arosa, Switzerland, at 6000 feet, and varieties of 
Melanargia galatea and Argynnis niobe, 2, taken on the 
Splugen Pass in July; also specimens from other localities 
for comparison.—W. J. Kaye: A fine example of the re- 
markable moth Dracenta rusina, Druce, from Trinidad. 
The species bears a wonderful resemblance to a decayed 
dead leaf, the patches on the wings suggesting the work 
of some leaf-mining insect.—E. M. Dadd showed a number 
of Noctuids common to the British Isles and Germany, and 
directed attention to the constant differences between the pre- 
valent forms occurring in England and the prevailing forms 
of the same species on the Continent.—Dr. F. A. Dixey: 
Specimens of Ixias baliensis, Friihst, and Huphina nerissa, 
Fabr., remarking that the association between the two 
species must necessarily be Miillerian, and not Batesian.— 
S. A. Neave: A number of Lepidoptera selected from the 
collection made by him in N.E. Rhodesia, in 1904 and 
1905, comprising the following rare and _ remarkable 
species :—Melanitis libya, Distant: Liptena homeyeri, 
Dewitz; Pentila peucetia, Hew.; Catochrysops gigantea, 
Trim. ; Crents pechueli, Dewitz, and Crenis rosa, Hew., 
which are evidently two distinct species; and Crenidomimas 
concordia, Hopff., the mimic of the last two species. Also 
two remarkable species of the genus Aphnaus—including 
the female, so rarely taken in this genus—Acraea natalica, 
Boisd., and Acraea anemosa, Hew., with two remarkable 
moths showing a close mimetic resemblance to them. The 
exhibitor further stated that his collection should prove 
interesting as regards seasonal forms, especially in the 
Acreine and Pierine, of which he showed additional 
examples. 
NO. 1933, VOL. 75 
Royal Microscopical Society, Octoter 17.—Mr. A. N. 
Disney, vice-president, in the chair.—Cornuvia serpula, 
a species of Mycetozoa new to Britain: J. M. Coon. For 
the first time a complete description was given of all the 
stages of this organism, previous descriptions being limited 
to the mature plasmodicarp and its contents. 
Physical Society, October 26.—Pro!. J. Perry, F.R.S., 
president, in the chair.—The strength and behaviour of 
ductile materials under combined stress: W. A. Scoble. 
In former tests of materials under combined stress either 
the ultimate strength or elastic limit stress has been con- 
sidered, and the tensions have been applied either directly, 
or by internal pressure in the case of thin tubes, so that 
the distribution of stress was approximately uniform. The 
present experiments were made on bars 3-inch diameter, 
subjected to bending and twisting to reproduce the irregular 
distribution of stress occurring in practice. The yield- 
point was selected as the criterion of strength, but it is 
open to more than one specification. Here the stress corre- 
sponding to the first sign of yield was not taken, but that 
given by the intersection of the two parts of the stress- 
strain diagram corresponding to perfect elasticity and com- 
plete yield, so that the intermediate state was neglected. 
The critical bending moment was found to be greater than 
the yield torque, 2660 and 2400 lbs. ins., and plotting the 
corresponding bending and twisting moments the ellipse 
gave the closest approximation to the  results.—The 
behaviour of iron under weak periodic magnetising forces : 
J. M. Baldwin. The behaviour of iron in strong 
alternating fields has been studied by many observers, and 
the induction in iron when placed in both strong and weak 
fields has been thoroughly examined by static methods, 
but up to the present no results have been published of 
the induction in weak alternating fields. The author has 
now, however, succeeded, by means of Lyle’s wave-tracer 
(for description of which see Phil. Mag., vol. vi., p. 549), 
in examining the induction in periodically varying fields 
down to extremely low amplitudes. The principal points 
brought out are as follows :—(1) the permeability satisfies 
a linear law through a considerable range for’ weak fields, 
diminishing to a minimum about 150 as the amplitude of 
the field diminishes; (2) as the field diminishes the differ- 
ence in phase between the induction and the magnetising 
force tends to disappear, and (3) at the same time the 
hysteresis losses become very small; (4) frequency at these 
low values of the field has practically no influence on the 
results obtained.—Fluorescence and magnetic rotation 
spectra of sodium vapour and their analysis: Prof. R. W. 
Wood. After recapitulating the descriptions of the ex- 
perimental arrangements given in previous papers, the 
author describes the work done during the present year in 
photographing magnetic rotation and fluorescent spectra. 
A 12-feet grating, a specially constructed three-prism 
spectrograph, and a monochromatic illuminator were used. 
Challenger Society, Octoher 31.—Prof. d’A. W. 
Thompson in the chair.—Preliminary note on a method of 
detecting successive moults of the same species among 
Crustacea: Dr. Fowler. The uncertainty of connecting 
together in series the successive stages of larvae captured 
in tow-net hauls is great, especially if the general form 
and appendages differ at different moults. Brooks noticed, 
twenty years ago, a curious numerical relation betweem 
the lengths of four specimens of stomatopod larva, which 
appears to be capable of expansion into a regular law, 
and if the larvze captured be sorted at first by general 
morphological similarity and by constant association in 
the same hauls, it seems probable that this law will give 
the key to their relationship. The author had measured 
and sexed more than 400 specimens of Conchoecia 
subarcuala, Claus=macrocheira, Miller. The males and 
females each fell into three groups when arranged by 
lengths; when the frequency of the lengths occurring in 
each group was plotted, each formed a small *‘ curve of 
frequency,’’ and the mean length of each group when 
multiplied by a certain factor (found experimentally) yielded 
the mean of the next highest group; the extremes, 
similarly multiplied, yielded, approximately, the extremes 
of the next highest curve. The factor is different for 
males and for females, and seems to be an expression of 
