386 
NATURE 
| NOVEMBER 27, I913 
Artemia, in 8 and 10 per cent. solutions, attained 
maturity without the introduction of extraneous food. 
The food supply was Chlamydomonas sp. in various 
stages of its life-cycle. The nauplius stages of 
Artemia die unless the brine contains a supply of free- 
swimming monads, but the adults live on the resting 
stages of the monads. The food supply present in 
the surface film is so great that Artemia spends much 
of its time feeding there, and it is probable that the 
habit of swimming on its back was adopted by 
Artemia as an adaptation for feeding in the surface 
film. In 4 and 5 per cent. and in 20 and 25 per cent. 
brine-solutions, either the eggs did not hatch or the 
young nauplii died as soon as the eggshell burst. 
Adults transferred from the optimum solutions (8 and 
Io per cent.) lived in the weaker and stronger brines, 
and the eggs laid by them lived. It was found that 
eggs would hatch in any brine solution in which 
they had been produced. No variation of the order 
described by Schmankewitsch was found; the tail- 
lobes were of uniform size in all strengths, and 
possessed the same number of spines. 
Pseudohermaphrodite Examples of Daphnia. 
Dr. J. H. Ashworth directed attention to four 
abnormal female examples of Daphnia pulex, in each 
of which the antennule of one side resembled that of 
a male. No other male secondary sexual character 
Was present, except that in one case the margin of 
the carapace presented almost the configuration of 
that of a male. The reproductive organs of all the 
specimens were normal ovaries, and were not para- 
sitised. The offspring of two of the specimens were 
examined and found to be all normal. 
Position of the Order Protura. 
Mr. R. S. Bagnall discussed the position of the 
order Protura, to the ‘‘abdominal feet” of which he 
did not attach so much importance as some authori- 
ties have done. While recognising the affinities of 
the Protura to the Chilopoda, he considered the 
relationship with the Insecta to be closer. 
Mr. Bagnall also gave a brief account of the hymen- 
opterous parasite, Thripoctenus russelli, found in the 
larve of the bean thrips, Heliothrips fasciatus. He 
also recorded Thripoctenus found in association with 
various thrips in several English localities, and com- 
mented on the economic importance of these parasites 
of thrips. 
Oviposition of a Fly on Centaurea. 
Prof. Hickson communicated a paper by Mr. ja 
Wadsworth on the oviposition of the Trypetid fly, 
Urophora solstitialis, on Centaurea nigra and allied 
composites. This fly possesses a highly developed 
piercing ovipositor, which, when fully extended, is 
nearly twice the length of the fly. During oviposition 
the abdomen of the fly is pushed down between the 
bases of the lowest and outermost bracts of the 
flower-head, and the piercing portion of the ovipositor 
is forced downwards and inwards towards the axis of 
the flower-head, and then gradually bends upwards 
until its tip is finally in the space between the young 
florets and the overlying bracts, in which space the 
ova are deposited. The larva, after hatching, bur- 
rows through the corolla of a young floret, travels 
down to the ovary, and feeds there, its presence 
causing the growth of a ‘ gall.” 
Observations on a West African Wasp. 
Prof. Poulton recorded observations by Mr. W. A. 
Lamborn, in’Southern Nigeria, on the wasp, Synagris 
cornuta, in the males of which there is remarkable 
difference in the grade of mandibular development. A 
NO. 2300, VOL. 92] 
male with very large mandibles terrorised four others — 
with smaller mandibles, and was thus successful in 
capturing a female (the case being one of marriage 
by capture), which emerged from a nest under Mr. 
Lamborn’s observation. Prof. Poulton suggested 
that the immense horn-like mandibles are a disadvan-— 
tage in obtaining food and perhaps in other ways 
in the struggle for life, and that the emergence of the 
females covers a period long enough for this struggle 
to tell, so that the males with small or rudimentary 
““horns"’ have the advantage in the end through the — 
operation of natural selection, while the others have 
the advantage at the beginning through sexual selec- 
tion in the form of battles between the males. 
Heredity of Melanism in Lepidoptera. 
Mr. W. Bowater described experiments on various 
melanic Lepidoptera. He pointed out that in Amphi- 
dasys betularia the melanic form is now more common 
than the typical form, and stated that a breeding 
experiment seemed to point to the Mendelian domin- 
ance of melanism in this species. He also recorded 
the results of pairings of typical and melanic examples 
of Odontoptera bidentata. He found that distinct 
segregation occurred, that homozygous and _hetero- 
zygous melanic forms were indistinguishable, that 
extracted types bred as true homozygotes, and that 
two heterozygous blacks, when paired, gave, in eight 
families, 75 per cent. black and 25 per cent. type. 
Mr. Bowater claimed that the specimens bred, 1800 
in number, proved that melanism in this species is a 
simple Mendelian dominant. 
Pseudacraeas and their Acraeine Models on Bugalla 
Island, Victoria Nyanza. 
Dr. G. D. H. Carpenter found that on Bugalla 
Island, in the Sesse Archipelago, Victoria Nyanza, 
there abounds a species of Nymphaline butterfly, 
Pseudacraea eurytus, which has several forms closely 
mimetic of various species of the Acrzine genus 
Planema. The 356 specimens of Pseudacrea caught 
by him in 1912-13 were excessively variable, inter- 
mediates between the various forms being as common 
as the types. Such intermediates are of the rarest 
occurrence on the mainland shore of the lake at 
Entebbe (twenty-five miles N.E. of Bugalla), but the 
typical forms abound there. On Bugalla Island the 
model Planemas are very scarce, probably from 
scarcity of the food-plant, so that their presence can 
be of little protective value to the Pseudacrzeas; hence 
any specimen which exhibits variation away from the 
type of the model has as much chance of escaping 
enemies as a form which closely resembles the model. 
On the mainland, however, Planemas are plentiful, 
so that their presence is of definite selective value for 
the mimics; consequently variations of the mimic are 
at a disadvantage in the struggle for existence, and 
are rarely found on the mainland, but the typical 
mimetic forms are abundant. It was claimed that 
this case afforded strong evidence of the reality of 
mimicry, and of the power of natural selection-to 
keep up the mimetic likeness. 
Geographical Relations of Mimicry. 
Dr. F. A. Dixey pointed out that certain definite 
schemes of colour and pattern in the wings of butter- 
flies are characteristic of certain definite geographical 
regions and even of smaller districts, and cited in 
illustration the well-known combination of red, black, 
and yellow Ithomiine, Heliconiine, Nymphaline, and 
Pierine butterflies in Central and South America. He 
remarked that it was natural to seek for an explana- 
tion in the direction of a common influence exercised 
by the geographical environment, but that this ex- | 
