Dwiglit.] 126 [Nov. 5, 



•when a minute piece was fortunately isolated, it, as a rule, immedi- 

 ately became dry and useless. Fig. 4, PL n., represents a fibre teased 

 out in glycerine; it shows that the black stripes are strongly drawn 

 together, that their granular structure is indistinct, and that the gray 

 bands are wanting. It is more or less obscured by the longitudinal 

 folds of the sarcolemma which give it a somewhat fibrillated appear- 

 ance. The particular fibre chosen is not an extreme case; on the 

 contrary, most fibres were much more obscure, and those in water 

 more contracted than those in glycerine. In the few specimens of 

 any value to which no fluid had been added, most of the fibres were 

 less normal than the one drawn, and I can remember but two indi- 

 vidual fibres that were decidedly more so. There can be little doubt 

 that if it were possible to examine the fibres of the larger water 

 beetles, in situ, that they would present quite different proportions 

 from those usually ascribed to them. 



The following are briefly the conclusions which the preceding ob- 

 servations appear to warrant. The fibre consists of a sheath, the 

 sarcolemma, and of a ground substance, in which elements wdiich 

 may provisionally be called granules, are imbedded in transverse 

 double rows. There is no reason to suppose that the difference be- 

 tween the white and the gray has any other than an optical cause, 

 namely : that the part of the ground substance nearest the black 

 bands receives not only the rays of light that would naturally strike 

 it, but others reflected or refracted, or both, from the black bands, 

 and which do not strike the middle of the space between the latter. 

 (Heppner, Schafer.) If this be admitted, it is merely a corollary 

 that, in contraction, the gray should disappear; as is the case. No 

 appearances have been seen that are suggestive of the handles of 

 Schafer's dumbbell-like rods, which, indeed (judging from the abstract 

 of his paper) , he has assumed rather than demonstrated. As has 

 been already stated, nothing like fibrillar structure is to be seen in 

 the living and healthy fibre. 



The sarcolemma is firmly attached to each edge of the ends of the 

 black bands, and the granules must, in some way, be prevented from 

 separating laterally, so as to give the support for the folds, into which 

 the muscle contracts. The ground substance is the contractile ele- 

 ment; it is also highly elastic. When the fibre is stretched all parts 

 become narrower, and when contracted, broader; but in the latter 

 case the change is chiefly in the ground substance. 



