180 MR. NEWPORT ON THE NATURAL HISTORY, ANATOMY, 



cates the purpose for which it is employed ; and the habits of the Melon larva, and its 

 mode of seizing and attempting to pierce the skin of the bee that conveys it to its nest, 

 confirm the conclusion deduced from the structure of its mandible. 



The gradual change of form which the mandible undergoes in the larva state, indicates 

 some modification of function even during the larva period. I have already shown that the 

 mandible in the adult larva is a short thickened corneous organ, more nearly resembling 

 that of the perfect insect : not as in that fitted for cutting and comminuting vegetable 

 tissue, nor, as in the very young, for piercing soft textures, but rather adapted for crush- 

 ing and bruising. The mode in which this organ is changed in its condition is, first, by 

 deciduation, at the change of tegument, of its terminal claw-like apex, exactly as the cor- 

 responding part of a true limb is thrown off at the change on the reduction of the legs to 

 mere tubercles, preparatory to their future re-development in the nymph or pupa in a new 

 form ; next, by the growth and enlargement of every part of the structure in a lateral, 

 and its retardation in an axial direction. The result of this change is a complete obliteration 

 and anchylosis, or permanent union of the whole in one powerful angulated structure, 

 which retains an articulation only with its parent segment. This is the mandible of the 

 adult larva. 



Changes, similar in principle and mode of operation, but carried to a far less extent, 

 take place in the other appendages of the cephalic segments of Meloe, the maxillae and 

 palpi, the function of which, like the structure, undergoes but little modification. 



The whole of the feeding-period of the larva state, in so far as refers to change in the 

 segments of the body, is scarcely other than one of simple growth and enlargement. 

 Change of form by aggregative development, as we have seen, commences in the append- 

 ages and parts of the head ; but the tegument of the segments in the larva still retains 

 its original flexible uniform condition, and is scarcely thrown into folds, even at the junc- 

 tion of separate segments. The nuclei of its component cells continue to reproduce, and 

 when the external layer becomes aged and resistant, obstructing the function of the in- 

 ternal, it ceases to be nourished and is removed. But as the entire body advances to its 

 maximum of size, certain forces become active in its internal structures, which lead to those 

 rapid and important changes of form in the whole which we recognise as the Metamor- 

 phoses of the Insect. 



Those structures which are the immediate agents of all voluntary and instinctive move- 

 ments, the muscles, are also those of the Metamorphoses. Nourished to the utmost while 

 the larva is feeding, they keep pace with the tegument in growth. They are connected 

 with the internal surface of the tegument in every part of the body, deriving their origins 

 from it, and having their attachments in it ; so that any alteration in them affects the 

 form of the portion they are connected with, and of the whole body, to a greater or less 

 extent in proportion to the degree of their contractility, and to the number and direction 

 of the muscles engaged. 



We are entirely ignorant of the secret cause which first excites these structures into 

 action in effecting the metamorphoses, at definite periods of the insect's existence, if it be 

 not, as there seems reason to suspect it is, allied to an accumulation, and subsequent dis- 

 charge, of force evolved during growth in the structures themselves, a vital endowment of 



