HARDWICKE'S SCIENCE-GOSSIP. 



11 



subcutaneous muscles which enable it to writhe its 

 way through the soil. Its body appears to be com- 

 posed of thirteen segments,* as follows; viz. — The 

 head, which consists of a hard horny shell bearing the 

 antenna; and the mouth-organs. The front portion 

 only is externally visible, the remainder being inter- 

 nal, and it is capable of being withdrawn more or 

 less by invagination within the following segment. 

 The head is followed by twelve segments, all covered 

 with a tough but yielding integument. The first 

 three of these are somewhat distinguished from the 

 others by being rather narrower ; they are also 

 marked in mature larvae with three pairs of whitish 

 spots on the ventral surface, and correspond, I 

 believe, to the thorax of the perfect insect. The 

 two last segments are so blended that it is some- 

 what difficult to distinguish them ; but in other di- 

 pterous larva; I have seen that the anus evidently 

 occupies the last segment but one, and the posterior 

 spiracles the last; and I believe this to be the case in 

 the present instance. 



I will commence my description of this creature 

 with some account of the integument, this being the 

 first structure that naturally presents itself to our 

 notice. I have given some attention to this part 

 of my subject with the view of recognizing the three 

 layers of integument called by Mr. Lowne the pro- 

 toderm, the mesoderm, and the endoderm.y I must 

 frankly state that I have failed in this endeavour : 

 the structure appears to me to differ in many re- 

 spects from his description. I must therefore beg 

 my readers to accept my statements as the best con- 

 clusion [ can at present draw from my observations, 

 but subject to revision at any future time, should I 

 find it necessary to do so. It appears to me, then, 

 that there are three distinct layers in the integu- 

 ments of the larva, — an external cuticular, an inter- 



* Mr. Lowne says that seventeen "is the typical number 

 of segments assigned on theoretical grounds to all true in- 

 sects, which always have the body in the perfect state divided 

 into three parts, the head, the thorax, and the abdomen, and 

 that the head consists of five of these segments. This is 

 doubtless correct, but for my presf nt put pose 1 have preferred, 

 with Burmeister, to regard the head as the first segment. 

 See Lowne's "Anatomy of the Blow-fly," p. 3, and Bur- 

 meister's " Manual of Entomology," Shuckard's translation, 

 1836, p. 35. 



t Mr. Lowne's remarks on the subject of the integument 

 will be found at p. g of his "Anatomy of the Blow-fly." They 

 are too long to give a fair summary of them here. Though 

 evidently intended to apply primarily to the integument of 

 the fly, I understand their main outlines to be applicable to 

 that of insects in general, as I gather from the opening pass- 

 age; viz., "the integuments of insects are usually said to 

 •consist of three layers, and these may be easily traced in the 

 fly;" and then he goes on to describe them as they are found 

 in that insect. The chief difficulty to which I refer in the 

 text is, that I cannot discern any cellular character in the 

 innermost layer, which appears, as I have stated, to be com- 

 posed of several lamina;, superimposed closely and generally 

 evenly one over the other. I should state that the instru- 

 ment I employ is one of Smith & Beck's popular micro- 

 scopes, furnished with li objectives, with which I have no 

 difficulty in making out most examples of cellular strncture. 



mediate mesh-like, and an internal laminated layer 

 Of these the first and the last occur over the whole 

 surface of the larva, the intermediate only on the 

 lateral portions. On examination with a lens, it wil 

 be seen that there are two broad bands, which I 

 shall call the lateral bands, one on each side of the 

 larva, where the integument differs in appearance 

 from that on the dorsal and ventral surface. On the 

 last-named portions, the skin, although crossed with 

 deep transverse folds, especially at the junction of 

 the segments, is comparatively smooth, while on the 

 lateral bands it is rather darker and of a corrugated 

 or puckered aspect. This difference of external ap- 

 pearance corresponds to a difference of structural 

 arrangement, and I believe of adaptability to the re- 

 quirements of the insect. The external or cuticular 

 layer, as before mentioned, is common to the whole 

 surface, and appears to be an almost structureless 

 membrame of a light amber-colour, the protoderm 

 I believe of Mr. Lowne. I have sometimes fancied 

 I could detect a cellular structure in it, but am un- 

 certain about this. On the lateral bands its surface 

 is puckered, as seen with a i objective, and is covered 

 with minute hairs (mere elevations I believe) 

 scattered irregularly over the surface, and pointing 

 backwards. On the dorsal and ventral surfaces, 

 however, it is much smoother, and the hairs here are 

 arranged in short groups or rows. Besides these 

 hairs, there are occasionally a few of a much larger 

 description, which arise from a cup-shaped basal 

 sheath, and present a fluted appearance when suf- 

 ficiently transparent. 



On, the lateral bands there are frequently deep 

 pits, corresponding to internal elevations, which 

 form points for the attachment of muscles. The 

 intermediate layer is confined to the lateral bauds, 

 and consists of a yellowish and apparently tough 

 dense tissue, with lozenge -shaped interspaces, 

 having a direction transverse to the length of the 

 baud, and giving it the appearance of a mesh or net. 

 This layer is closely adherent to the outer one first 

 described ; indeed, I have only been able to sepa- 

 rate the two accidentally, and over very small 

 portions, yet sufficiently to show their distinctness. 

 1 scarcely know how to regard this tissue, but am 

 inclined to think that its structure is somewhat 

 similar to that of cartilage, in which soft trans- 

 parent cells are separately imbedded iu a harder, 

 semi-transparent, intercellular matrix. On one 

 occasion 1 found, on tearing it away from the sub- 

 jacent laminated layer, that the surface of the latter 

 was covered with little eminences, corresponding in 

 size and order of arrangement with the clear inter- 

 spaces above them ; and if my view is correct, these 

 would be the cells torn from the interspaces, 

 through being perhaps more Grmly adherent to the 

 layer beneath them than to the matrix by which 

 they were surrounded. This subjacent layer is the 

 innermost and the thickest of the three which 



