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to that assigned for the complicated teeth of the Butterfly, &c., namely, because it possesses powerful masticating organs at the mouth, and here we find it to consist of a number of straight, sharp, siliceous teeth, of very insignificant proportions (Pl. III. fig. 4), which are discernible only under a high microscopic
From the stomach the food passess into a short intestine, narrow at first, and widening as it proceeds downwards. About the middle, this intestine receives a number of tubular glands, known as the biliary tubes" (Pl. VII. fig. 1, d), which correspond in some degree to the liver in vertebrate animals, and pour out their fluid upon the food in its passage through the intestine. Further on, this canal becomes much wider, and is then known as the "colon" (Pl. VII. fig. 1, e), which is the termination, not only of the intestine, but of the whole digestive system. The remaining parts of the apparatus are not of sufficient interest to the general reader to induce us to dwell upon them, and we shall therefore pass on to that remarkable and deeply interesting portion of the Bee's anatomy, the respiratory system.
The Bee, in common with most other insects, does not breathe as we do through apertures in the head, but the air is admitted by special organs situated upon the surface of the body. These are called spiracles or stigmata, and consist of little holes pierced in the external integument, two pairs being
situated on the thorax, and a pair upon each ring of the abdomen.
In the common Housefly, these spiracles are very beautifully formed, the entrance being partially closed by a great number of ramifications of the external covering of the body, proceeding from the circumference of the spiracle, and forming a delicate network, the object of which is to prevent particles of dust from entering along with the atmosphere. the Bee, however, the contrivance is of a different kind, consisting of two elongated apertures, one behind the other (Pl. VII. fig. 3), and the outer one only provided with a number of short hairs for the purpose of precluding foreign substances, instead of the beautiful ramifications that are present in the Housefly.
Through these spiracles or breathing-holes, then, the air is admitted into special organs which enable it to circulate through the body (Pl. VII. fig. 2, ad b,&c.*), and consisting of a number of sacs or bladders that communicate with one another, and with the external atmosphere, by means of wonderfully constructed tubes, called trachea.
The distribution of these sacs and tubes is deserving of especial attention, and we must ask you to accompany us in an examination of the plate representing this portion of the insect's anatomy (Pl. VII. fig. 2, a a'd', and b bb, &c., the part drawn in tint).
* The respiratory system is represented by the large sac and connecting tubes at the left side of the figure.
In explanation, however, it is necessary to remark that, although only one set of organs is here delineated, they are bilateral, that is to say, distributed in pairs symmetrically on either side of the body. The largest pair of sacs is found in the abdomen (Pl. VII. fig. 2, a); from these proceed two main trunks, the one (b) upwards into the thorax, and the other (c) down to the termination of the abdomen. The latter gives out large branches ending in sacculi or little sacs (d), whilst the tubes that pass upwards (6) traverse the thorax in a straight line without any ramification whatever, and only in the head do we find a second pair of sacs (a) of considerable dimensions. You will see, therefore, that the greater number of the respiratory vessels are to be found in the head and abdomen, especially in the latter, and the reason for this arrangement is simple and instructive. The abdomen contains all the viscera, and is by far the heaviest part of the body; it has therefore the greatest need of the inflated air-vessels to give it support, and to some extent this applies also to the head with its large solid eyes, whilst the thorax is effectually buoyed up in the atmosphere by the powerful double wings: thus, you see, the equilibrium is maintained throughout every part of the body.
Not only has Nature been thus far consistent in the disposition of the respiratory vessels, but we find that in the queen-bee, which quits the hive and takes her flight in the air only twice or thrice during her
lifetime, and whose abdomen is necessarily filled with an immense number of eggs (Pl. VIII. fig. 1), the large respiratory sacs are quite wanting, and the only air-vessels are the larger and smaller trachea.
But by far the most remarkable feature in connexion with this portion of the Bee's anatomy is the structure of the tracheal tubes themselves. On examining one of these under the microscope (Pl. VII. fig. 4), you will find it to consist of a double membrane supported between the two folds by a coil of hair-like fibre, just as the coil of wire gives strength to the elastic gas-tubing employed to feed a tablelamp from an ordinary chandelier. The object of this arrangement is similar in both cases: the trachea are rendered very elastic, and any hindrance to the passage of air by their collapse is only momentary, as the supporting coil reopens the tube as soon as the external pressure is removed. A close investigation of this mechanism shows that the fibrous coil becomes more and more delicate as the trachea diminish in size, and that it is not continuous, but here and there a new coil commences between the folds of the preceding one.
Dismissing now this interesting portion of the Bee's anatomy, we shall direct our attention to the nervous and circulating systems, and we must commence by remarking that in the Bee, as in all other articulate animals, the relative position of these two systems is precisely the reverse of what it is in the higher animals. In the latter (taking ourselves as an example),
the spinal chord, with its nervous ganglionic centres, will be found to traverse the dorsal region of the body: they run, in fact, along the back, whilst the heart is situated in front; but in the Bee the central nervous chord passes along the ventral portion, whilst the tubular heart occupies a place immediately within the integument of the dorsal surface. The circulating apparatus consists chiefly, so far as anatomists have hitherto been able to trace it, of what is called the dorsal vessel (in consequence of its running along the back of the body). This dorsal vessel assumes the form of a tube, attached to the outer integument by bands or ligaments, and that portion of it which is situated in the abdomen is divided into eight chambers, communicating with one another by means of valves so constructed as to admit of the blood passing in one direction only, that is to say, towards the head. After it has traversed the abdominal chambers, which may be compared to the chambers of our heart, the sanguineous fluid continues its course through the thorax, where the dorsal vessel forms a simple contractile tube (the aorta) without any divisions, and thence it is forced into the head and other parts of the body.
The circulation of the Bee cannot, however, be completely traced, nor is it, so far as we are able to judge, of a perfect character; for, although it has been stated by some anatomists that a portion of the blood is conducted back from the head to the posterior part of the body by means of a smaller tube situated