76 THE AMERICAN MONTHLY [March 



difFereutiated amphibian and for that reason these points 

 may differ in the more generalized forms. 



The turtle representing the reptiles, differs from the 

 frog (Fig. 5). The muscle fibres appear in transection 

 a little more angular and the diameter is smaller. An 

 average of twenty measures 55 microns, in the turtle. 



77 per cent of the nuclei are imbedded in the sarcous sub. 

 stance. This shows and advance in one line, over the frog. 



The pigeon is considered next (Fig. 6). This animal 

 though not belonging to the highest class of mammals be- 

 longs among warm blooded animals. Naturally differences 

 are to be expected between this and the coldblooded forms. 

 The first difference noted is that the fasicles are more 

 distinct. The average diameter of twenty fibres is 24 

 microns. The nuclei are found to a great extent at the 

 edge and only 3 per cent are imbedded in the sarcous 

 substance. 



Turning to the mammals, one finds still more differ- 

 ences (Fig. 7). The fasicles in the rabbit are much 

 more distinct than has yet been found and are surrounded 

 by more connective tissue. In section, the individual 

 fibres are far more angular, making the form more pris- 

 matic than cylindical, — an average of 20 diameters 25 

 microns, less than one-half the size of the frog. The 

 rabbit's fibre has only J per cent of its nuclei imbedded 

 in the sarcous substance. This leaves by far the greater 

 number at the edge, projecting out, even push out the 

 sarcolemna. The cat's muscle is very like that of the 

 rabbit though there is more connective tissue between the 

 fasicles and also between the fibres themselves. This 

 may be due to the greater activity and strength in the 

 cat than is possessed by the domestic rabbit, necessitat- 

 ting a large blood supply and firm binding of parts to- 

 gether. An average of 20 fibres in diameter measures 

 24 microns, and none of its nuclei are imbedded in the 

 sarcous substance. 



