AND DEVELOPMENT OF MELOE. 173 



always continuous with the external layer of the tegument, and is thrown off with it at 

 each change. Whether the spiral fibre of the trachea, which is in the course of formation, 

 originates, as believed by Platner, in the nuclei of cells, I am not prepared to affirm ; but 

 from the existence of nuclei in those which compose the walls of these cavities, it is pro- 

 bable that such may be the case. 



The tegument of the head affords some peculiarities of particular interest. The cells 

 are smaller and more uniform in size and shape than on the body and limbs, and measure 

 each less than one two-thousandth of an inch in diameter. But those which cover the 

 antennae are much larger, and are as irregular as those on the legs. The eye (fig. 10), 

 which, as formerly shown, is a single structure in this stage of Meloe, fitted only for 

 near vision, has its large projecting cornea formed entirely of layers of perfectly trans- 

 parent dermal cells, which are continuous with those that cover the parietes of the 

 head, but are somewhat smaller, and measure about one three-thousandth of an inch. 

 Those which form the circumference, and general surface of the cornea, are each slightly 

 convex, and are all of the same size, like the corneales in the compound eye of the 

 perfect insect * ; while the centre of the cornea, the focus of the line of vision, is occupied 

 by a single cell, much more projecting, and more than twice as large as the others. This 

 condition of the cornea in the young Meloe, although perfectly distinct, is very difficult 

 to observe, owing to the circumstance that as yet the cells constitute only portions of one 

 nearly uniform transparent tegument of a single organ, and are not freely isolated, as is 

 the case with the corneales in the imago. It is from this cause that these presumed 

 embryo corneales in the larva can only be detected when the object is placed on its side, 

 and when a high power of the microscope is employed. 



This is the condition of the external portions of the tegument. When the young animal 

 has been a few days from the egg, the deeper-seated layers of cells have in part united 

 longitudinally, and constitute a fibro-cellaeform structure, which gives attachment internally 

 to the muscles ; while the external layers continue to grow and be reproduced as distinct 

 cells. The internal layers thus constitute the true dermo-skeleton. This may assist to 

 explain what I have yet to demonstrate ; that the organs of support which exist in the 

 interior of the body in the perfect insect, strong bone-like processes, which give attach- 

 ment to muscles, and which in some parts support and protect the nervous centres like 

 the vertebrae in Chelonian reptiles, are solidified portions of the common tegument ex- 

 tended inwards, and consolidated during the metamorphoses of the insect. 



Each segment of the dermo-skeleton in the imago, as shown by the late Professor 

 Audouinf, is made up of distinct pieces, the separate development of which is but slightly 

 indicated in the very young larva. Some of them, however, are marked in the head and 

 thoracic segments. In the head a triangular suture is extended forwards in the middle 

 line of the dorsal surface, between the eyes, and, diverging on either side to the antennae, 

 marks its fine of union in the ovum. The prothorax, meso-thorax, and metathorax, are 

 also marked by a median dorsal sulcus, indicating the original individuality of the two 

 sides in the embryo, and their junction after the last parts of the yelk have been received 



* 



See Remarks on the Origin of the Ocelli, Linn. Trans, vol. xx. p. 342. 

 T Annales des Sciences Naturalles (prem. aerie), torn. i. 1824. 

 VOL. XXI. 2 A 



