262 Prof. L. C. Miall and Mr. T. H. Taylor on the 
surface of the exposed part is strongly chitinised, and 
serves for the prehension of food. In the young larva it 
is armed with three hook-like teeth, one median and of 
larger size, the other two smaller and further back. This 
chitinised ventral plate, which, although it is deeply cleft 
behind, is apparently singte, is replaced in older larve by 
two unequal oral plates, enclosing the mouth-opening 
between them, and each carrying two hook-like projections. 
Muscles pass from the body-wall to the oral plate or plates, 
and effect the movements necessary to mastication. In 
young larve, but not in older ones, a pair of curved 
chitinous struts, standing off on either side at right angles, 
probably serve to hold the plate in position (they are 
omitted from fig. 3). The upper-surface of the head is 
almost entirely concealed; on the minute exposed part 
are several small oblique sunk rods of chitin, of unknown 
function. The head-capsule, which answers to the wall of 
the head in more normal insects, consists of a delicate 
cuticle, lined by an epidermis. It is continuous with the 
oral plates, but otherwise completely immersed ; nothing 
can be seen of an invagination-cavity. Muscles pass from 
the body-wall to the head-capsule. There is also an 
endocranium, which we suppose to have originated in 
chitinous apodemes; it consists of an anterior median 
piece, deeply grooved on its upper-surface, and a posterior 
forked piece, divided into right and left halves, each of 
which gives off dorsal and ventral arms. The groove on 
the median piece lodges the pharynx. 
The Nervous System.—The central nervous system 
(fig. 3) is lodged in the thorax and the fore-part of the 
abdomen; it consists of cerebral ganglia and a ventral 
complex. From the latter paired nerves are given off to 
the head (three pairs), to all the thoracic segments, and to 
the first eight abdominal segments. A pair of large 
ganglia in front of the cerebral ganglia may represent the 
optic lobes of the blow-fly larva. The prothoracic and 
mesothoracic nerves have ganglia at their roots. No 
sense-organs have been clearly made out in the young 
larva, though in older larve minute structures, which are, 
probably sensory, appear on the exposed surface of the 
head (fig. 5). 
The Alimentary Canal—The mouth-opening leads into 
a small buccal cavity, which lies within the oral plate. 
The fore-part of the pharynx is strongly chitinised, and 
