ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 165 



transverse branches, by means of which the contractile substance 

 all along the end of the intestine is woven into a physiological 

 continuity. If the last posterior segment of a fly is torn away 

 with forceps, the end of the intestine will usually be left hanging 

 from it, and if examined while fresh in - o / Q NaCl solution, 

 exhibits lively peristaltic movements : peristaltic waves run 

 every few seconds at tolerably regular intervals from the mouth 

 of the Malpighian tubes towards the rectum. The waves at first 

 spread so quickly that it is impossible to detect the details of 

 the process. But if the preparation is left for a quarter to half 

 an hour, or pressed down with a tolerably heavy cover-glass, the 

 contraction is transmitted more and more slowly, the waves follow 

 at longer intervals, and may be clearly seen to spread themselves 

 over the single fibres and connecting processes. ' If, shortly 

 after a wave of contraction has reached the lower end of the 

 opening of the intestine, this end is mechanically stimulated with 

 the point of a needle, an anti-peristaltic wave instantly runs up 

 the fibres of the muscle, to the opening of the Malpighian tubes, 

 if not previously arrested by meeting a wave spreading from 

 above downwards." It is also noticeable that the conductivity 

 of the contractile substance itself appears to be temporarily much 

 depressed by the process of contraction. A wave starting after 

 a long rest spreads with apparently uniform rapidity from its 

 point of departure. But if another wave had immediately pre- 

 ceded it, the new excitation only produces a localised contraction, 

 or at most a wave that quickly diminishes and dies out near its 

 starting-point. 



The intestinal tract of some Fishes (Tench, Colitis) is well 

 known to contain a similar arrangement of striated muscle-fibres; 

 whether there are analogous relations of conductivity also has not 

 yet been determined (26). On the other hand, the conductivity 

 of the contractile tissues of certain Medusas (e.g. Aurclia') has been 

 thoroughly investigated, with results in complete accordance with 

 those yielded by cardiac muscle (27). 



The multiform complexes of smooth innxclc-ccUs exhibit com- 

 plete agreement with these mononuclear, striated muscle-cells, 

 in regard to conductivity of excitation. Here, again, it is to 

 Engelmann (28) that we owe the most important conclusions. 

 The ureter of many mammals (rabbit, guinea-pig, rat, etc.) is 

 peculiarly suited to exact investigations, as it offers a delicate 



