222 



On the arrangement of the Striations of 

 Voluntary muscle Fibres in Double Spirals. 



By O. W. TiEGs, M.Sc, 



Department of Zoology, University of Adelaide. 

 [Read September 14, 1922.] 



Plate XII. 



While examining the muscles of the larvae and adults of 

 a small parasitic wasp, Nasonia, I noticed, recently, that the 

 striations were not disposed transversely, as is supposed to 

 occur universally in voluntary muscle, but that they were 

 arranged in the form of a double spiral. The structure of 

 these muscles will be referred to more fully in a later paper. 



The purpose of this note is to draw attention to the fact 

 that the striations of voluntary muscle fibres, which histol- 

 ogists are unanimous in regarding as truly transverse, are in 

 reality likewise disposed in the form of double spirals. I have 

 observed this in the muscle fibres of the crayfish Astacopsisy 

 in the leg muscles of a South Australian grass-hopper, and 

 in the voluntary muscles of the much studied water-beetle 

 Dytisciis. 



Amongst mammals I have observed it in the muscles of 

 the rat, the pig, the dog, the rabbit, the mouse, and, finally, 

 in human muscle fibres, and its presence in such widely 

 separated groups suggests its universal occurrence. 



In a well-stretched fibre this double spiral arrangement 

 of the striations is relatively easy to detect, and is shown in 

 fig, 3, taken from the muscles of man. In such muscles it is 

 possible to begin at one end of a fibre, and focussing up 

 and down to travel along the spiral. Muscle fibres, however, 

 are usually examined in the contracted condition ; under these 

 circumstances it is often extraordinarily difficult to detect 

 the spiral nature of the striations. Two methods may, how- 

 ever, be adopted : — 



(1) If a muscle fibre has been well flattened, the stria- 

 tions at the sides of the fibre may actually be observed to 

 bend downwards and out of the plane in which the striations 

 on the upper portion of the fibre have apjDroximately lain. 

 This condition, taken from a muscle in the dog's tongue, is 

 shown in fig 4. Generally, however, the striations are so 

 very close together that it is possible only with the greatest 

 difficulty to notice the small change in direction taken by 

 the turn of the spiral. 



