222 E. A. Schäfer, 



be on]}' a short one, so that there is no real reversal of the striae. 

 Nor do the appearances seen in polarized light assist the view originali}' 

 advocated by Merkel. What other explanation then can be offered for 

 the apparent reversal which takes place in the living muscle in con- 

 traction? We have seen that in the living and moderately retracted 

 muscle-segment there is an appearance of dim and bright striae simu- 

 lating sarcous elements and the clear intervals of the alcohol muscle, 

 but that the bright striae are in reality due to a different cause, viz: 

 to the light reflexion which occurs at the membranes of Krause. 

 When the muscle contracts the sarcous elements become bulged out 

 at the expense of the fluid of the clear intervals which probably passes 

 into their pores; they therefore approach the membranes of Krause, 

 becoming shorter in proportion to the amount to which they undergo 

 bulging, and the intervals between the successive membranes of Krause 

 are lessened. As the intervals thus lessen a point is at length reached 

 at which the bright borders, which are due to light reflexion from the 

 surfaces of the membranes, blend with one another in the middle of 

 each segment, The narrowed interval therefore between each two 

 membranes of Krause now looks wholly bright although, as the alcohol 

 preparations show, it still contains the shortened and bulged sarcous 

 element. On the other hand, these membranes appear as dark lines 

 alternating with the narrow bright band thus produced, the dark and 

 light effects respectively being enhanced as the result of the alternate 

 bulging and constriction which characterize the contracted sarcostyle. 

 These are the changes which can be seen in the contracted sarcostyles 

 of the wing-muscles as compared with their appearances in extension. 

 As for the fibre itself (or bundle of sarcostyles) all that need be 

 remarked regarding it, is the obvious fact that the sarcoplasm 

 is increased in amount opposite the constrictions of the contracted 

 sarcostyles at the expense of that which is opposite then- bulgings. 



We may now consider the cross-striation of the ordinary muscles. 

 The causes of the production are even more difficult to be arrived at 

 than in the wing-muscles by reason of the fact that another element 

 has to be taken into consideration viz: the nodes and filaments of the 

 transverse networks. Indeed, in the ordinary acid- gold preparations 



