402 SEA-SIDE STUDIES. 



are of two kinds, striped and unstriped, the 'former 

 being generally, but erroneously, called voluntary, the 

 latter involuntary muscles. According to recent re- 

 searches, it has become evident that the striped muscle 

 is only a more differentiated form of the unstriped, 

 there being several intermediate stages between the 

 two * In the preparation I have made of the ventral 

 chord of the dragonfly larva, this is strikingly exhibited. 

 A fragment of muscle is attached, the fibrillse of which, 

 instead of being striped (all the muscles of insects are 

 of the striped kind), are partly striped, partly unstriped ; 

 that is to say, in the same bundle some of the fibrillse 

 are without the transverse markings, and those fibrillse 

 which have such markings have them only part of the 

 way down, the remainder of the fibrillse being unstriped. 

 This is not only interesting as a fact in muscle develop- 

 ment, but presents a striking analogy to the development 

 of nerve-fibres, which we here see in the same trunk 

 partly emerged from their primitive granular condition. 

 I conclude, therefore, that the difi*erentiation of nerves 

 shows the following phases : 1st, As in many Molluscs 

 and all embryos, a granular homogeneous mass ; 2d, 

 As in insects, and perhaps Crustaceans, a linear dispo- 

 sition of the granules into fibres, but without an in- 

 vesting sheath ; 3d, Fibres, or rather tuhules, differing 

 from the preceding in structure, having each an envelop- 

 ing sheath, which isolates one fibre from the other, so 

 that the nerve becomes a fasciculus of tubules.i* 



* Leydig, Histologie, p. 43. 



t Stilling, op. cif. p. 11-13, decides that all primitive fibres have an 

 investing sheath ; but unless he would deny the claim of those named 



