540 HENRY M. BERNARD, 



wing mechanism is not a great amount. On the other hand, the con- 

 traction of the anisotropous layers would be an additional and com- 

 plicated element in the mechanism of contraction almost inconsistent 

 with extreme rapidity. It seems to me that the additional amount of 

 contraction thus gained would be very slight and very costly. 



In this connection it is interesting to note that the dice-box shape 

 of "element" of these wing muscles (Fig. 25), which seemed to me so 

 distinct under the microscope (cf. also Retzius' figures) ^), do not ap- 

 pear in Schäfer's photographs at all. I would like to suggest that 

 the dice-box shape is due to the isotropous substance running a short 

 way down the anisotropous pits, which may be its normal position, 

 ready to flow in either direction for contraction or for expansion. 

 Some of Schäfer's photographs (2, 2 a, 4, 4 a) show the exact reverse 

 of the dice-box shape. The distal ends of the anisotropous substance 

 seem to have collapsed, as if the isotropous substance had been drawn 

 out of them in extreme expansion (cf. the extreme expansion in Cru- 

 stacean muscles, Figs. 5, 6, 7, 8). 



From these observations and measurements it seems that the 

 whole contraction of the muscle „element" can be accounted for by the 

 movements of the isotropous substance, and that the anisotropous layer 

 takes no direct active share in the contraction of the fibril, but only 

 indirectly causes the contraction by absorbing the isotropous substance. 



III. 



The third question is: Can the anisotropous layers be considered 

 as masses of nuclear substance attracting the clear protoplasmic sub- 

 stance, Verworn having shown this to be a probable explanation of 

 the movement of contraction in living Rhizopods? 



According to Schäfer, this absorbing anisotropous substance is 

 comparable with the staining spongioplasm of a living cell. The 

 essential similarity of this with Verworn's theory needs no insistence. 



Experimental evidence as to the nature of the anisotropous sub- 

 stance was clearly difficult to obtain. Fig. 4 suggested to me an ex- 

 hausted muscle perhaps being regenerated from a large nucleus; 

 whether it will bear such an interpretation or not I cannot say. I 

 therefore tried to experiment with exhausted muscle. 



I caught a number of large Blue- bottles — Musca vomitoria. 

 Some were kept resting under glass, the others, one at an time, I 



1) Biologische Untersuchungen, Bd. 1, tab, 15, figs. 23 and 27. 



