HARDWICKE'S SOIKNCE-GO SSIP. 



15 



is a layer of large soft nucleated cells, roughly hexa- 

 gonal, and reminding one of those between the 

 coats of the oesophagus. With respect to the 

 functions of the several parts of the alimentary 

 canal as above described, I can say but little with 

 certainty ; but there are some remarks which I feel 

 tempted to make. Burmeister* states that the 

 chyle in insects is a ''whitish, greenish, or even 

 brownish thick liquid, which first presents itself 

 as a flocky substance between the innermost and 

 second tunics of the stomach, and upon a microscopic 

 investigation appears to consist of minute globules." 

 This corresponds very well with the dark brown 

 liquid I have always found in the proventriculus 

 and stomach, and which I therefore regard as the 

 chyle. This fluid is the ultimate produce of the 

 digestive act, and in the higher animals it is absorbed 

 into the general circulation by the lymphatic vessels 

 placed along the small intestine. As insects are 

 not provided with lymphatic vessels or veins, it is 

 evident that absorption must in them take place 

 directly through the walls of some part of the in- 

 testinal canal ; and Burmeister states that it has 

 been observed to take place through the walls of the 

 stomach.f In this insect, at all events, I think that 

 it must do so, for if not, it must pass either through 

 that portion which intervenes between the opening 

 of the bile-tubes and the large gut, or else through 

 the walls of the latter organ itself. Now the mem- 

 branous and muscular walls of the former portion 

 seem too thick and impervious to allow of this, and 

 the latter organ is generally quite full of dry excre- 

 mentitious matter, and in neither part do I find 

 any further trace of the fluid in question. I there- 

 fore think that the functions of digestion and 

 absorption, which in the higher animals are per- 

 formed respectively by the stomach and small 

 intestine, are here carried on in the common cavity 

 of the proventriculus and stomach, perhaps indif- 

 ferently in either, for I cannot discern any difference 

 of structure in the two that should lead me to think 

 otherwise. 



It may be noticed that I have abstained from 

 naming those portions of the intestine which succeed 

 the opening of the bile-ducts, and I have done so 

 because I am not quite certain how to regard them. 

 The portion that intervenes between the bile-ducts 

 and the large gut seems to me to correspond in 

 position, though not in function, to the small 

 intestine in the vertebrate animals, the sphincter 

 representing the valvular aperture known as the 

 ileo-csecal valve, and the large gut, with its caecum, 

 answering to the large intestine or colon with its 

 caecum. But I find that, Mr. Lowne, in his "Ana- 

 tomy of the Blow-fly," speaks of the evidently 

 corresponding portions of the intestine of that 

 insect, as the large intestine and the rectum respec- 



P. 36S. 



t P. 368. 



tively.* I do not know why this is, and cannot 

 quite reconcile myself to regard the latter huge 

 cavity as the rectum, which term signifies the latter 

 portion only of the colon in vertebrates, viz. that 

 immediately preceding the anus. The functions of 

 the salivary glands and the bile-tubes are generally 

 thought to be the secretion of fluids analogous to 

 those from which they take their name. It does 

 not occur to me that I can say more with advantage 

 on this subject at present. 



The digestive organs are entirely surrounded by 

 a web or rete of loose tissue, apparently consisting 

 of large flat cells, adhering to each other by their 

 edges. Mr. Lowne, speaking of this tissue, says 

 that a store of elaborated nutriment is laid up in it 

 for the development of the pupa.f This tissue 

 hangs, as it were, attached to the bight of the sali- 

 vary glands, and the bile-tubes lie close to its inner 

 surface. Its colour is generally white, but near the 

 anus I have frequently found it yellow, in which 

 cases also 1 have distinctly seen that its colour is due 

 to oily particles within the cell, which, so long as 

 the cell wall is unbroken, remain separate, but 

 when pressed out of the cell, ruu together. Where 

 the white colour prevails, the oily particles are 

 much smaller, assuming the form of globules, and 

 their colour is lost. The whiteness, I think, results 

 from their minute dispersion in the contents of the 

 cells, in the same way as the whiteness of milk is 

 due to the presence of the butter globules. On one 

 occasion I found that the globules were remarkably 

 deficient, the rete being rendered to a great extent 

 transparent and invisible from their absence. Por- 

 tions of it, however, were filled with a brilliantly 

 white substance, which, under the i glass, was 

 seen to consist of a vast number of transparent 

 cells, containing a grauular, mulberry-like mass. 

 Opposite the lower end of the stomach, there may 

 be seen, in some larvae, two spindle-shaped bodies, 

 intimately connected with the inner surface of the 

 rete. They consist of membranous sacs, filled 

 with nucleated cells, which present traces of seg- 

 mentation. The sac has a fine duct connected with 

 it, which I have not traced. These are the rudi- 

 ments of the future ovaries. The testicles in male 

 insects are also seen as spherical sacs, containing 

 the immature spermatozoa. 



A. Hamjioxd. 



(To be continued) 



" The attempt to construct a universal globe, 

 implies that we shall not only have a precise know- 

 ledge of the events which have occurred at any 

 particular point, but we shall be able to say what 

 events, at any one spot, took place at the ssme 

 time with those at any other spot." — Prof. Huxley's 

 Lectures. 



* Lowne's " Anatomy of the Blow-fly," p. 5/. 

 t Ibid., p. 29. 



