618 
near the Oxford University Parks, and on the following day I 
captured eleven more in the same place. There had been ex- 
céptionally heavy rain, extending over some days, immediately 
previous to those on which I found the specimens, and it there- 
fore seems probable that these animals are driven out of the 
earth when it becomes sodden with moisture. Thus it is pos- 
sible to account for the capture of a very unusual number of 
specimens, for, as far as I can learn, the species has hitherto 
only been met with singly in this locality. 
I have also ascertained what happens to the animals when 
the earth in which they are contained becomes hard and dry 
fromthe loss of water. A few of the twenty-two specimens 
were killed and hardened, and the remainder were put in a box 
containing earth, in which they buried themselves. In the press 
of other work the box was neglected, and remained untouched 
in my laboratory until to day, the earth having quickly dried 
into a hard cake. To-day I emptied the box, and fully expected 
to find the slugs dried up dead, but to my surprise I found 
twelve specimens alive, each encysted in a thin transparent cap- 
sule formed of the hardened mucous secretion of the animal’s 
skin. The body was contracted, and oval in shape, but it had 
been so completely protected from evaporation that there was 
no noticeable reduction in bulk after these hottest months of the 
year, during which water had been entirely withheld. One or 
two specimens had died almost immediately after capture, and 
a few escaped, so that all those which had been exposed to the 
heat and dryness in the box had become encysted, and survived 
in apparent health. Epwarb B. PouLTON 
Wykeham House, Oxford, October 19 
Lepidoptera and Migration 
THE subject of migration in connection with Lepidoptera is 
beginning to receive some attention at the hands of our best 
lepidopterologists. I am decidedly of opinion that the abundance 
or scarcity of many species of Lepidoptera is largely regulated 
by migrations from abroad. Last year our southern shores were 
visited by an abnormal number of rare Sphzzyide, but this year 
there have scarcely been any records of captures published con- 
cerning them. It would be interesting to know what are all 
the influences which cause these migrations, and if there is a 
periodicity to the phenomenal occurrences. 
Birmingham, October 12 W. Harcourt BATH 
The Earthquake of October 16 in the Vosges, &c. 
May I be allowed to call attention to the fact that Alsace lies 
on the direction of the great circle, ‘‘ boundary of Tertiary 
formation of the United States,’ mentioned in my letter which 
appeared in your number of the 14th inst. (p. 570), and further- 
more that Strasburg has been repeatedly shaken since 1355, the 
first date which I found recorded as having been marked by a 
shock. It is quite true that the interval between that shock and 
the next recorded (1556) was 201 years ; but the greatest subse- 
quent interval, that between the shocks of 1577 and 1655, was 
only of 78 years. This interval represents a multiple of 13, 
being = 13 x 6, The interval of 13 is of frequent recurrence, 
as I purpose to show in a paper which I have about terminated 
on this question of intervals and periods of earthquakes. 
J. P. O’ REILLY 
Royal College of Science for Ireland, Stephen’s Green, 
Dublin, October 23 
RECENT ORNITHOLOGICAL WORKS 
HE future student of British birds ought to have little 
difficulty in working out the distribution of species 
within the shores of Great Britain, so much excellent 
work having been done in the way of local lists during 
the last few years, and certainly one of the most useful 
will be the little work on “ The Birds of Cumberland and 
Westmoreland,” just issued by the Rev. H. A. Macpher- 
son and Mr. W. Duckworth.! The situation of these two 
counties is interesting, especially to the student of migra- 
tion, and the notes on the passage of water-birds and 
sea-birds are particularly good. The completeness of the 
t “‘ The Birds of Cumberland critically studied, including some Notes on 
the Birds of Westmoreland.” By the Rev. H. A. Macpherson, M.A., and 
William Duckworth. (Carlisle, 1886 ) 
WATORE 
[Oct. 28, 1886 
information, and the concise and simple form in which it 
is conveyed, render this small book a model of what a 
faunistic work should be, and it forms a worthy accom- 
paniment to the many excellent county lists of birds which 
have appeared in England during the last twenty years. 
It would be well if every expiring species in Great Britain 
had had its death-song as well sung as is the case with 
the Dotterell, by Mr. F. Nicholson, in the present work. 
While Protection Acts are spreading their gis over many 
birds in the breeding season, so that the numbers are 
visibly increasing, and the enlightened care of a few 
landed proprietors aids the work of bird-preservation, 
there are still a certain number of species whose nesting 
days in this country are numbered, and which, like the 
Great Bustard and the Bittern, are doomed by the inexor- 
able advance of civilisation to seek less over-crowded 
countries in which to breed. The (too probably final) 
breeding of the Dotterell in Cumberland is therefore 
appropriately described by Mr. Nicholson, who has 
himself taken the eggs in the county. An excellent 
account is likewise given of the breeding of the Pied 
Flycatchers. 
We learn with some surprise that the White-headed 
Long-tailed Titmouse of Scandinavia, the true Acredula 
caudata (Linn.), “may be detected in Cumberland in 
mid-winter,” when “the appearance of a flock of adults 
in their snow-white caps is refreshing to an insular ob- 
server.” We should like to see some of these Titmice, 
and may state that an example is a desideratum to the 
national collection, where we should be glad to receive a 
specimen. Our experience in France, where we have 
shot ad/ three races of the Acredula caudata, is that it is 
impossible to detect the difference of the forms when in 
the open, though a difference in note led to our recognis- 
ing A. 7rbiz. We can only consider the true A. caudata 
to be a very occasional, though not impossible, migrant 
to our shores, and we by no means sympathise with the 
authors of the “Birds of Cumberland” in their sup- 
pression of the name of Acredula rosca for the British 
Long-tailed Titmouse, from a dislike to the “needless 
multiplication of species.” As regards Great Britain the 
facts are perfectly plain. The resident Acredi/a is always 
recognisable, and the white-headed form is only a very 
occasional winter visitant, and however much they may 
interbreed in the Rhine Provinces or elsewhere on the 
Continent, there is nothing of the kind in England, where 
perfect differentiation exists; and therefore to say that 
our English Long-tailed Titmouse should be called Acre- 
dula caudata of Linnzus, is a mistake and nothing else, 
for that name belongs to the Swedish form. Those 
ornithologists who continue to do this suppress a most 
interesting fact in nature, viz. that the isolation of the 
British Islands from the rest of Europe has produced a 
well-marked modification in the colour of some of our 
birds, amounting in certain instances to a subspecific value, 
The same reasoning applies to the Coal Titmouse, where 
our authors state that “ British specimens have generally 
olive backs, as contrasted with the slate-gray backs of 
typical German specimens, but intermediate forms 
occur.” This is not our experience. In summer plumage, 
when the olive-brown tips and the feathers become shed, 
the back of the English Coal Titmouse is gray, and then it 
is difficult to tell it from a summer-plumaged /. a¢ey from 
the Continent. But if two winter-killed birds are com- 
pared, the difference between the British and Continental 
specimens is very strongly marked, for the back in the 
latter remains gray, whereas in the British form it is olive- 
brown. Having been the first, as we believe, to detect 
this modification in the British form, we have, ever since 
we first gave it the name of Parus britannicus, assidu- 
ously collected a series of specimens in the British 
Museum, and we have never seen reason to modify our 
original opinion, nor have we yet seen the intermediate 
forms for which our authors vouch. 
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