AND DEVELOPMENT OF MELOE. 179 



undergone but little alteration in form from that of the very young, like which it is 

 marked with a longitudinal and a triangular sulcus. The eye, which in the embryo 

 larva is a single organ, is now a compound one, formed of three facets on each side of the 

 head. In this multiplication of parts it resembles the eye in the lower Myriapoda, the 

 Julidce, in which the eye, commencing as a single structure, becomes at its first change a 

 triple one*, preparatory to future subdivision to form the compound eye of the imago. Up 

 to this period the antenna has undergone less change than any other structure of the 

 head, thus proving that, whatever is its function, it is exercised in precisely the same 

 manner in the adult as in the very young larva. But it is in the parts of the mouth that 

 the greatest changes of form have occurred ; changes which lead us to infer a change in its 

 economy. The mandible of the adult larva, as I have formerly stated, is a short strong 

 corneous organ, totally different from that of the embryo larva. It is in this that the 

 mode of development by anchylosis, or complete union of originally separate parts, in the 

 formation of one structure or body, is most distinctly shown. The mandible in the ori- 

 ginal formation of the embryo in the egg is the true and legitimate appendage of, at least, 

 one of the basilar segments of which the entire head is composed, and which segment is 

 identical in its mode of origin with the other segments of the body. This fact I had the 

 honour of announcing in the ' Transactions' of this Society, as discovered in the embryo of 

 Geophilusf; and although it has been somewhat questioned by Prof. Erichsonf, I have 

 since been enabled to verify it repeatedly, not only in the Myriapoda, but also in the 

 embryos of true insects — for example, in Forficula. To trace the formation of the man- 

 dible, therefore, we must regard it as the articulated appendage of a single segment, — in 

 fact, a true limb in its origin and structure, but which, gradually altered in its condition 

 and form, becomes adapted to a particular function, and to variations in the mode of its 

 employment in that function. The changes in this structure usually take place in ani- 

 mals at so early a period, often, as in the whole of the Vertebrata, even during the earliest 

 stages of the embryo, that we are unable to follow them, and satisfy ourselves of the fact 

 of their occurrence. But this is not the case in the lower forms of Articulata, the Myri- 

 apoda, nor even in Meloe and many other hexapods. In the embryo of the vermiform 

 Myriapoda, as in Geophilus, every segment of the body is furnished with a pair of append- 

 ages, and this also is the case with each of the segments of the head. These appendages 

 originate at the sides of each segment as minute tubercles, one pair to each. Those which 

 belong to the head appear first, but are followed in quick succession by those of the 

 anterior segments of the body, and sooner in proportion to their proximity to the head. 

 No difference is at first recognizable in any of them, either in form or size ; but after a 

 period more or less brief, according to the type and species of animal, the mandible 

 becomes enlarged and changed in its appearance. In the Chilopodous Myriapoda it retains 

 the articulated pediform structure throughout the entire life of the animal, and is em- 

 ployed as an organ of prehension rather than of manducation. This is precisely what we 

 have already seen in the very young Meloe, which has a mandible jointed and pediform in 

 structure, and penetrant and prehensile in function. The structure of an organ thus indi- 



* Phil. Trans. 1841, p. 127. t Linn. Trans, vol. xix. p. 289. 



X Reports on Zoology for 1843-44 (printed by the Ray Society); Entomology, by Dr. W. F. Erichson, p. 409. 



