ox THE MICROSCOPIC AXATOMY OP AN INSECT LARVA. 609 
ated above tlie intestine (fig. 1, /) (in our figure the larva is 
represented on its back_, as it very frequently appears when 
swimming)^ and commences near the first in the second 
segment_, and extends to the end of the tenth. Its walls are 
completely transparent and colourless^ as is also the fluid 
which it contains ; and it therefore requires a little focusing 
and a good object-glass to see it well. Near the commence- 
ment of each segment, if the contractions and dilatations of 
the heart be watched, a small lipped orifice on either side of 
the vessel will be seen to open and shut, the lips playing the 
part of valves ; beneath each valve on either side is a large 
transparent cell (fig. 7 ) ; and again another pair of cells 
before the next valve is reached. These bodies appear to bo 
nerve-cells, destined to control the movements of the heart. 
The number of contractions of any one part of the heart in a 
minute appears to be about twelve. The movements of the 
vessel can be easily watched, and the opening and closing of 
the valves, and the structure of the presiding ganglia, form 
most interesting objects for study. 
Muscular system . — The muscles of the Corethra larva, like 
the other parts of its organization, are quite transparent, and 
readily admit of observation. Their striped structure is easil}^ 
observed. Those connected with the moveable appendages 
of the head can readily be isolated and named ; but with re- 
gard to the muscles of the other segments of the body, there 
appears to be a general repetition of form and arrangement. 
Oblique muscles pass from one segment to another, crossing 
and inter-crossing so as to constitute a mechanism whereb}^ 
those rapid jerks and spasmodic actions may be produced, by 
means of which locomotion is effected. In the eleventh seg- 
ment a long muscle is perceptible, by means of which the 
lateral plume is elevated or depressed, the bases of the hairs 
which form it being connected with this muscular band. The 
muscular fibre of the heart and alimentary canal is of the 
unstriped description, as in higher animals. 
Nervous system . — The nervous system in this little larva 
consists of supra- and sub -intestinal portions. The supra- 
intestinal portion is placed in the first segment (fig. 1, //,), 
behind the eye (/) . It consists of two large ganglia, which 
send nerves to the eye and other parts of the head. A great 
number of minute tracheary tubes ramify on the smTace of 
these ganglia. They are connected by two bands of nervous 
matter, with the first sub-intestinal ganglion, which is situated 
at the anterior end of the second segment, closely attached to 
the pharynx. This ganglion is oval in shape, and sends off no 
large branches but the two commissures ; it is connected by a 
commissure of nervous matter with the second sub-intestinal 
