CONSIDERATIONS. 123 



Those muscles which pass directly from one part to another 

 without the intervention of tendons, are mostly pyramidal or 

 cylindrical, according to the form of the parts to which they are 

 attached. Those which have tendons are either conical, pyra- 

 midal, pseiido-penniform ; that is, flat, triangular, with the fibres 

 arising from the same line, and attached to one or both sides of 

 a flat tendon, — penniform, where the fibres, not arising from 

 the same line, give the muscle a wedge-shaped and notched 

 appearance, — or compound, that is, formed of several heads, 

 which are each furnished with a tendon, these tendons before 

 their insertion uniting into one. 



One remarkable circumstance in the organization of insects 

 is, that many muscles have their origin from, and are inserted 

 into, two perfectly moveable parts of a quite different nature. 

 These are not merely muscles, which move parts forming a 

 series, as the vertebra of the higher animals, or the segments 

 of the abdomen in insects ; these are muscles which move certain 

 parts with relation to one another ; but those to which we refer 

 move the parts in relation to the trunk, the fixed part of the 

 body, yet arise from parts equally moveable, and of a quite 

 different function. In the Coleoptera, and also in not a few 

 other insects, many very powerful muscles are thus situated. 

 Such is the extensor posticus alee, which is at the same time 

 the extensor coxa metapedis. 



Observation proves that, in the Articulata, the presence, 

 volume, and even the form of the muscles, depend solely on 

 the function of the part they move. Hence it arises, that 

 when, in any species, a part loses its power of motion, without 

 undergoing any other change, the muscles usually inserted 

 thereto disappear to yield place to more important organs ; 

 and when a part changes its form or function, we find the muscles 

 inserted into it equally vary in volume, and even in their dispo- 

 sition to accommodate themselves to the new function : a simple 

 modification in the articulation of the moveable part some- 

 times varying its motions very considerably, the muscles in- 

 serted into it are modified in consequence of this change. 

 Lastly ; it may happen, that the piece to be put in motion 

 varies its functions ; the muscles also change theirs. 



Moreover, observation proves, that the parts from which the 

 muscles arise, may vary much in form and size without the 

 muscles being at all influenced thereby ; and that analogous 



