Dicranura vinula, and other Notes. 115 
structing its cocoon. Prof. Poulton (12) has already 
pointed out that the freshly-made cocoon while still 
moist is strongly acid, which observation [ can amply 
confirm. Moreover, if a larva is watched when spinning 
itis at once seen that the aperture of the prothoracic 
gland is brought into close proximity with that of the 
sik glands, and further that the former is constantly 
‘moist. I interrupted a larva in this occupation, and by 
means of a fine roughened pair of forceps caught the end 
of the thread projecting from the silk-gland aperture ; I 
then held the larva against a glass slide which was flooded 
with formic acid, and drew the thread into the acid; the 
larva continued to discharge the silk as I gently pulled 
the thread out. The first portion of the thread, which 
was dry and hard when I seized it, remained unaltered, 
but the portions following passed at once into the formic 
acid, swelled a little, and adhered firmly to the glass 
and also to those portions of the thread with which they 
came in contact, for I was able to draw out several inches 
of silk and to coil it up and down the slide. I then 
removed the glass slide, and substituted another free 
from formic acid. The silk which was drawn out on to 
this slide adhered feebly to the glass, did not swell, nor 
did the various lengths adhere to one another, but I was 
able to lift from the slide a fine thread of fibrous silk in 
no way partaking of the gelatinous character which had 
been assumed by that which had been led into formic 
acid. 
In order to put the matter beyond doubt I tried to 
prevent the formic acid from being employed in the con- 
struction of the cocoon. By means of blotting-paper and 
fine glass tubes I endeavoured to remove all the formic 
acid from the glands of a few larvee which had just begun 
to spin up. ‘Ihe handling necessary for this so disturbed 
the larvae that in most cases they died without pupating, 
only one of them succeeded in pupating, but not one of 
them made any further attempts at spinning. I therefore 
abandoned this method in favour of neutralising the 
acid. Two larve ready to spin were placed in a glass 
vessel whose sides and bottom had been moistened with 
a solution of sodium carbonate ; no materials were given 
for incorporation with the cocoon. Both these made 
cocoons which were very similar to those usually con- 
structed in the absence of wood-chips, etc., but at those 
