62 SCVZIN (Clg. 
and as warnings from danger, when guiding their vessels 
in a fog or in darkness; and sail-echoes of sounds from 
their own vessels are always to them warnings of possible 
danger of collision. The cases which I have mentioned, 
however, are all of a special and accidental character. 
That is, they are special because they are connected only 
with fog signals, and accidental because they depend 
upon the fortuitous movements of sail vessels. 
Cases of the projection of sail-echoes of the sounds of 
fog signals into pseudumbral areas, like those suggested 
for montumbral areas, will probably not be numerous, 
but both kinds of cases are worthy of careful investiga- 
tion, not only because of the inherent importance of the 
subject to which they relate, but because they are inci- 
dental sources of danger which have been introduced by 
the establishment of fog signals. 
THE ENEMIES OF LEPIDOPTEROUS PUPA EN- 
CLOSED IN BARK-FORMED COCOONS. 
BY EDWARD B. POULTON, M.A., F.R.S., HOPE PROFESSOR OF 
ZOOLOGY IN THE UNIVERSITY OF OXFORD, ENGLAND. 
Tue beautiful and perfect concealment of the cocoons 
constructed out of bark by many species of Lepidoptera 
has often attracted attention and admiration. In some 
species, such as the British Acronycta leporina, the larva 
tunnels deeply into the bark, constructing a chamber at 
some distance beneath the surface, and carefully removing 
the bark-dust formed by its building operations. The 
mouth of the tunnel is closed by fragments of bark spun 
together so as to form a covering exactly flush with the 
surrounding surface, which it also resembles in texture 
and color. In other species a natural crack or furrow in 
the bark is selected by the larva and is similarly covered 
in level with the bark around. In the genus Cerura 
(Dicranura) the larve excavate an oval area which is 
covered in by a more or less domed roof, similarly 
built of pieces of bark so well fitted and woven together 
that the appearance is exactly that of some rounded, 
flattened or irregular projection on the trunk of the tree. 
Furthermore, in the choice of situation it is usually found 
that increased aid to concealment is afforded ; the ap- 
parent projection being formed on an appropriate part of 
the trunk, and with due regard to the existence, arrange- 
ment and direction of the irregularities of its surface, 
such as furrows, etc. Those who believe in the efficiency 
of Natural Selection in evolution will probably regard this 
interesting method of concealment as the outcome of 
countless generations during which the attacks of enemies 
have been, on the whole, more successful against the pro- 
ducts of less perfected instincts, and less so against those 
of the more perfected. Furthermore, we must suppose 
that the increasing perfection in instincts has acted se- 
lectively on enemies, sharpening their faculties, until, by 
action and reaction, the present high level of constructive 
skill has been reached, and is maintained. 
How far is it possible to gain evidence of such a rela- 
tionship between enemies and prey ? At first sight, one 
of the cocoons I have described appears to be so perfectly 
concealed as to defy the sharpness of any enemy, however 
acute. But observation, especially directed to this end, 
will show that such an inference is incorrect. 
On April 12 of the present year I was examining the 
bark of a black poplar (Populus nigra) near Yoxford, in 
Suffolk, and found a cocoon of the ‘‘ Poplar Kitten” 
(Cerura bifida) which had evidently been recently opened 
by some enemy, almost certainly a bird, and the chrysalis 
extracted. The edges of the opening were still brown 
and fresh, as was the interior of the cocoon ; and the 
’ Vol. XXIII. No. 574 
larval skin remained fresh and untouched inside. The 
opening was in the middle of the exposed surface and not 
at one end, as it is when the moth emerges. Besides, the 
cocoon had been opened and cracked by a blow from some 
hard object such as a bird’s beak, and the sharp irregular 
margins were quite different from those of the natural 
opening made by the moth, doubtless by means of a cor- 
rosive fluid, as in the allied species, Cerwra Vinula, which 
Mr. I. H. Latter has recently shown to secrete caustic 
potash for this purpose. Furthermore, the moth emerges 
far later in the year, and, hadit emerged at an exceptional 
time, the empty pupal skin would have been left behind 
in the cocoon. We may therefore safely assume that the 
opening was the work of an enemy, and, as the cocoon 
was five feet from the ground, it was probably due to some 
tree-creeping, bark-exploring species of bird. i 
After the hint supplied by this observation I found that 
such instances are quite common and that a considerable 
proportion of these cocoons are thus opened and their 
contents abstracted. It is probable that the attention of 
the enemy is directed to any cocoon-like object by the 
sense of sight and that the object is then tapped, and, if 
found to be hollow, opened and the pupa devoured. If I 
am right in supposing that the pupa has to run the gaunt- 
let of such dangers as these, it follows that any careless- 
ness in construction or in the selection of a site would 
tend to be eliminated, and we are able to picture to our- 
selves, with a considerable degree of probability, the kind’ 
of conditions under which this wonderful form of pro- 
tective concealment has been developed and is now main- 
tained. 
These conclusions are perhaps capable of being brought 
to a crucial test, and, as this involves much time and 
much observation, it is to be hoped that several naturalists 
may attack the question. During the winter and spring 
a large number of such examples should be collected and 
noted, with special reference to the degree of concealment 
exibited by the opened cocoons as compared with those 
which are found to have escaped attack. ‘The subjective 
element would require to be checked by calling in the aid of 
others who are ignorant of the point under consideration but 
possess the requisite accuracy of eye. Attention should 
only be paid to fresh cocoons which have been opened in 
the season of the observation ; for the old battered cocoons 
of past seasons will be commonly found on the trunks. It 
may be that the problem demands too large a number of 
examples to be capable of solution in this way ; but on 
the other hand it is possible that positive evidence may 
be forthcoming. 
AN OBSERVATION ON THE TERMINAL VERB 
IN INFANT SPEECH. 
SCRIPTURE, NEW HAVEN, 
BY E. Wi. CONN. 
Ir has sometimes been asserted that the most natural 
position for the verb is not at the end of the sentence, 
and that children would not of themselves separate the 
participle or infinitive from the auxiliary or main verb, as is 
done in German syntax. I wish to record a personal ob- 
servation to the contrary. 
The child, W.S., twenty-nine months old, has not 
learned any language but English, and has not heard any 
sentences constructed otherwise than according to correct 
grammatical rules. W. S. was told to ask for some money 
to buy shoes, but in doing so said, ‘‘ I want some money 
for my shoes to buy.” Upon the question ‘‘ What ? ” the 
sentence was repeated without change. On other occa- 
sions W. S. uses the words in the customary order, e. ¢., 
“Ym going buy new shoes.” The observation seems to 
prove that the terminal position of the infinitive is at 
least not unnatural, 
