DEVELOPMENT OF THE ALIMENTARY CANAL. 430 
the stomodzal portion of the alimentary canal opens into the 
mesenteron, but the insects drink greedily an hour after they 
emerge from the pupa. The crop is first distended with fluid, 
but if the insect is fed on coloured syrup this passes into the 
chyle stomach as soon, or almost as soon, as the insect is able 
to fly. 
I believe the lumen of the cesophagus communicates with the 
chyle stomach as early as the middle of the pupa state, and 
there is apparently a continuous lumen at least two days before 
the insect emerges from the pupa, although no fluid ever passes 
back from the chyle stomach into the cesophagus during the 
latter days of the pupa stage. 
Development of the Salivary (Sericterial) Glands.—So far as I 
know, no direct observations are extant as to the manner in 
which these glands are developed in the egg, but they are 
usually regarded as invaginations of the epiblast of the labium 
or of that at the root of the maxilla or mandibles, and they are 
seen as open epithelial tubes at an early stage of development. 
In the pupa, the tubular salivary glands of the imago of the 
Blow-fly are developed according to Kowalevski [145] from 
imaginal cells, which, he says, are found at the junction of the 
duct and gland sac of the larva. Van Rees [147, p. 76] differs 
widely from Kowalevski in his account of the manner in which 
the sericteria of the larva disappear, for whilst the latter states 
that they remain attached to their duct until after the develop- 
ment of the head, Van Rees figures and describes a new duct 
at this period which terminates in a blind end in the basal part 
of the proboscis, and says the degenerated gland masses are 
already separated from their ducts. 
I have carefully examined the new duct, and in young nymphs 
it is certainly not seen in transverse sections, except near the 
distal part of the rostrum. It appears to me to be an entirely 
new formation, having no connection with the larval sericteria. 
At a later stage, such as is represented in Pl. XXI., the blind 
end of this duct is connected by solid cell strings, which 
surround the cephalo-thoracic nerve cord with two masses of 
cells, one on either side of the cesophagus. It is from these 
29 
