On the structure of cross-striated muscle, 193 



facts, there would still be a serious difficulty in understanding' why 

 the existence of mere linear streaks of what is unquestionably material 

 of the softest and most labile nature should tend to cause so regular 

 a cleavage as that which occurs in muscle. But if as will presently 

 appear, these apparently linear streaks are in reality the optical ex- 

 pression of longitudinal planes intersecting one another, there need be 

 no call for such an effort of comprehension as the reticulum theory 

 requires. On the other hand, the failure of the crushed living fibre 

 to break up into longitudinal elements is not a serious difficulty to 

 the pre-existence theory. For if it be assumed that the substance ot 

 the muscle-columns during life is of a soft or semi-fluid nature, that 

 they are bounded only by a delicate pellicle, and that the inter- 

 columnar substance or sarcoplasm, although chemically different, is 

 also semi-fluid or fluid and in very small amount, it is only to be ex- 

 pected that on the rupture of the sarcolemma by crushing or manipu- 

 lation, the semi-fluid substance of the columns would tend to flow out, 

 as is actually seen to be the case. 



It is, however the wing-muscles of insects which unquestionably 

 afford the firmest support to the pre-existence theory and the strongest 

 evidence against the reticulum-enchylema hypothesis. I have already 

 explained why these muscles cannot be left out of consideration or 

 treated as a form of contractile tissue sui generis, but must be looked 

 upon as a variety of true cross-striated muscle which in all essential 

 points agrees with the more ordinary variety. They are composed of 

 muscle-columns or sarcostyles, which themselves show indications of longi- 

 tudinal striation, and which are separated from one another by inter- 

 columnar substance or sarcoplasm, agreeing with that of the ordinary 

 muscles in the manner of its behaviour to reagents and gold-staining, 

 and only differing in its relatively larger amount and in containing 

 larger and more obvious granules. Being thus present in considerable 

 quantity in the interstices of the sarcostyles, it presents no distinct 

 enlargements corresponding with the dots and transverse networks of 

 the ordinary fibres, although it is clear that wherever the sar- 

 costyles are constricted, as they are liable to be opposite the inter- 



Intemationale Monatsschrift für Artat. u. Phys. VIII. 13 



