90 MR. NEWPORT ON THE ANATOMY AND DEVELOPMENT 



more muscular structure than the great digestive cavity, which longer retains its cellae- 

 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 fife, 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 

 cellseform condition, its muscular tissue being completed very late. In Ichneumon (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 Microgaster the small intestine (g) and colon (h) are ready to convey the faeces 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 

 organs in the perfect Ichneumon, although he correctly believes in their existence. The 

 Malpighian structures (k), 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 larvae, 

 in which the food requires greater elaboration to assimilate it with the animal tissues, than 

 in the carnivorous feeder, which imbibes the ready-formed animal juices of another body. 

 In Monodontomerus, the Malpighian organs, even at the close of the feeding period, still 

 exhibit evidences of their original mode of formation by the longitudinal junction and 

 coalescence of cells to form tubes ; while in Ichneumon and Microgaster these parts are 

 more early and more extensively developed, although even in them they are incomplete. 

 On the contrary, in the true vegetable-feeding larva?, the herbivorous caterpillars, these 

 organs exist well-formed almost from the period at which the insect leaves the egg and 

 begins to feed ; and, in many instances, have their secretory capacity increased by the deve- 



