ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 63 



sluggish contraction in warm-blooded muscles. We have already 

 alluded to the peculiarities, especially the abundance of sarco- 

 plasm, by which the striated muscles of the bat are distinguished. 

 Experimental excitation, with single induction shocks, shows that 

 the process of contraction in these conspicuously " dark " muscles 

 (pectoralis major, biceps, and triceps) is remarkably sluggish. 

 Eollett reckons an average of 0-025 sec. for the latent period, 

 0'146 sec, for the ascending period of the curve, - 350 sec. for 

 the descending period, i.e. 0'496 sec. for the total contraction. 

 Hence these muscles appear more sluggish than any in the frog, 

 but quicker than those of the tortoise, quicker than the red 

 muscles of rabbit, but much slower than pale muscle in the same 

 animal. The differences in the contraction process of anatomically 

 separate muscles in the same animal are very striking also in 

 many invertebrates. Ch. Eichet (9) found very different curves 

 of contraction in the tail and claw muscles of the crayfish, whether 

 the contraction was discharged centrally or by artificial excita- 

 tion. The curve of the tail-muscles is short, and similar to the 

 gastrocnemius contraction of the frog. The adductor of the claw, 

 on the other hand, described an extended curve, which differs 

 essentially from that of the tail-muscles. This statement once 

 more tallies with the normal movements of the parts in question 

 (rapid napping of the tail, sluggish but protracted closing of the 

 claws). The greatest disparity in this direction might be ex- 

 pected between the wing and other body-muscles of insects, for 

 the wide histological differences between them are an a priori 

 indication of corresponding functional modifications. Unfortu- 

 nately there are no adequate observations as to the contraction 

 process in the former ; it is only known that they do contract 

 with extraordinary rapidity. Rollett has recently communicated 

 some interesting experiments on the physiological divergences 

 in muscles bearing the same name, but histologically different, in 

 insects (beetles) which are otherwise very similar (10). The 

 skeletal muscle-fibres, collectively, of Dytiscus differ fundamentally 

 in structure from those of Hydrophilus, while each beetle possesses 

 a perfectly uniform structure of its own muscle-fibres. Dytiscus 

 exhibits in a cross-section the flat muscle-columns, and correspond- 

 ing radial arrangement, of Cohnheim's Area?, from which the 

 rays of sarcoplasm stream out featherwise from the large accumu- 

 lation round the nuclei (Fig. 25). Hydrophilus, on the contrary, 



