90 MR. NEWPORT ON THE ANATOMY AND DEVELOPMENT 
more muscular structure than the great digestive cavity, which longer retains its celle- 
form condition, its lining cells becoming changed into secreting or glandular structures, of 
two kinds; one of which elaborates the juices required for digestion of food, while others 
take up the results and diffuse them through the body for the general purposes of 
nutrition. 
Hence we find that the general form of the great digestive cavity is very similar in all 
embryos of a given class, at the earliest periods; and similar in all which pursue a like 
habit of life, as in Hymenopterous parasites ; the chief structural differences being in those 
parts which become small intestine and colon. Different species, even among the para- 
sites, differ slightly in regard to these parts, both as to form and as to period of completion. 
In Monodontomerus we have found that the whole of the digestive canal long retains its 
cellæform condition, its muscular tissue being completed very late. In Zchneumon (fig. 8), 
and Microgaster (fig. 11), which feed within the body of their victims, the intestinal por- 
tion (g, h, i) of the digestive apparatus is completed more early, and a canal, paved with 
epithelium, is formed in it, but continues almost completely closed, and does not admit 
into it a particle of the matter to be rejected until the growth of the parasite is complete. 
In Mierogaster the small intestine (g) and colon (h) are ready to convey the feeces more 
early than in Ichneumon; and this seems to have some reference to the special require- 
ments of this species for a more early rejection of the waste of nutrition. In like manner 
the more or less early completion of the appendages of the digestive apparatus in the 
advanced growth of the embryo, or of the larva, immediately precedes the unfolding of 
some speciality of function or of instinct. I have already shown, in the first part of this 
paper, that the earliest completed glandular organs connected with the digestive apparatus 
in the larva of Monodontomerus, are the salivary. So we find also in Microgaster (fig. 11), 
in which they are not only early, but most extensively developed (d), for the production 
of that abundance of silk which is formed by this larva in the construction of its cocoon 
quickly after it has issued from the body of the insect it has devoured. In Ichneumon 
Atropos also, I have found the salivary organs (d) extensively developed in the larva at 
an early period, doubtless for a similar purpose. Dufour was unable to detect these 
organis in the perfect Ichneumon, although he correctly believes in their existence. The 
Malpighian structures (4), attached to the commencement of the intestinal portion of the 
digestive apparatus, and the function of which is still a question with some physiologists, 
although usually believed to be that of the liver, are completed, as we might fairly have 
anticipated, at a much later period in these parasites than in the vegetable-feeding larvze, 
in which the food requires greater elaboration to assimilate it with the animal tissues, than 
MI e pr en. 
exhibit evidences of their original mode of f tion b pers zen en 
re = of formation by the longitudinal junction and 
more early and more ante eiue dinge gr ws un‘ 
Où te eps the mat y ES aee although even in them they are incomplete. 
organs exist BEER ee Fe = on ——— 
bor to fel ae: à m the perie at which the insect leaves the egg and 
; and, In many instances, have their secretory capacity increased by the deve- 
