TRANSACTIONS OF THE LINNEAN SOCIETY. 137 
metamorphosis, lose their legs, and emerge as grubs not 
altogether unlike those whose places they have usurped. 
When an insect is destined throughout life to exist in the 
same manner and to use the same food, then it leaves the egg 
with the principal organs constituted in the same manner as 
in the imago.” 
Several apparent exceptions to this are cited, and a satis- 
factory explanation of most of them is afforded. 
Having thus described the degree of change which takes 
place after birth, the manner in which it is effected is next 
considered, and shown in great measure to depend upon the 
circumstance whether the organs undergoing change continue 
or not in a state of functional activity. It is rendered ob- 
vious that, in the former case, the changes must be slow and 
gradual, so as not to interfere too much with the performance 
of the functions; whilst in the latter they may be rapid, and 
accompanied with only one or two changes of skin, though 
necessarily accompanied with a period of quiescence. This 
is well exemplified in the instance of Lepidoptera, “‘in which 
a mouth originally mandibulate is destined to become suc- 
torial. Any gradual change in such a case would be incon- 
venient or impossible; the insect might starve in the mean. 
time. Here, therefore, it becomes desirable that the change 
should be rapid.” 
III. On the Hairs of Carcinas menas. By W. C. 
M‘Tntosh. 
This communication is an elaborate account of the appear- 
ance and structure, as seen under the microscope, of the 
hairs, or, more properly speaking, hair-like appendages found 
on different parts of the surface, both external and internal, 
of the common shore-crab, and as such will be interesting to 
the microscopist ; more so, in fact, to him than to the physi- 
ologist, for there is no attempt made, which is much to be 
regretted, to conjoin with the morphology some account of 
the physiological peculiarities which they doubtless possess, 
of these appendages. The tactile or sentient property pos- 
sessed at any rate by many of the hairs in the Crustacea has 
already, however, been the subject of various memoirs by M. 
Lavalle, Holland, Heckel, and more especially of Mr. Camp- 
bell de Morgan, who has shown conclusively their intimate 
relation to the nervous system. 
Dr. M‘Intosh appears to entertain doubts as to the audi- 
tory functions of the peculiar organ at the base of the internal 
antenne, but in this we think there is now but. little room 
for dispute; . bis) mine 
