24 
POPULAR SCIENCE REVIEW. 
ing from tlie margin of the spiracle at its superior extremity. 
The contraction of this muscle presses the valve which hears it 
upon the other, and thus closes the spiracle. 
It was originally intended to pass in review the whole of the 
structure of this insect, internally as well as externally. The 
subject, however, has run out to a greater length than was 
anticipated, and we must refrain at present from pursuing it 
further. 
The study of the development and anatomical structure of 
insects affords a vast extent of unbroken ground to many whose 
means of becoming acquainted with the broader aspects of the 
science of Entomology is, from various causes, limited to the 
observation of the familiar insects around them, and the 
extraordinary beauty and interest of the details which may 
thus be revealed may well prove the strongest incentive to 
master the drier technicalities of the subject which have 
occupied much of our attention in the preceding pages. Every 
part of insect structure will, on attentive examination, be found 
replete with what we may still delight to call Creative design. 
Does the House Fly or the Crane Fly sip its food by means 
which so long as they are unknown can excite but little in- 
terest ? Dissect them, and the secret of the process is revealed 
in a pumping instrument, which the skill of the mechanician 
can scarcely approach. With a view to facilitate the acquire- 
ment by the reader of a personal acquaintance with some of 
these interesting subjects, the following observations are offered 
as the result of the author’s experience. That patience and 
perseverance are necessary, it is scarcely needful to mention, as 
there is no royal road to knowledge of any kind. A certain 
amount of skill in drawing is highly desirable as a means of re- 
taining observations made, which if committed to memory alone 
would certainly be lost. Insects for dissection should be col- 
lected, not as single specimens, but a dozen or two at a time, when 
opportunity offers ; and if it is not convenient to make use of 
them at the time, they should be preserved in methylated spirit 
till wanted. By this means their internal parts are preserved, and 
the bleaching and hardening which they undergo is frequently 
an advantage, as it serves to render the nervous and muscular 
tissues more easily traced ; but this should not supersede the 
dissection of fresh specimens. The internal organs in all cases, 
and sometimes the external parts, should be dissected under 
water. A compound microscope, such as may be purchased for 
51 ., is desirable ; and a dissecting microscope, similar to that 
recommended by the late Dr. Lawson, which, together with a 
suitable set of dissecting instruments, may be obtained from 
Collins for a trifle. The stage of this instrument is provided 
with a gutta-percha trough, to enable objects to be pinned 
