DoNAi.DsON-ScHOEMAKER, Netvoiis System of Frogs. 125 



frog, plainly contains individuals in which the legs are incom- 

 pletely grown. But after virescens has acquired a weight of 

 about 5 grms., the relations characteristic of maturity are seen 

 to be attained. 



In the case of virescens, just as in catesbiana, the weight 

 value of the leg muscles undergoes a slight but steady decrease 

 as the frog gains in body-weight. This of course, means that 

 the body is increasing in weight at a somewhat more rapid 

 rate than are the legs. 



For^the'next comparison the three small frogs which con- 

 stitute the Group I as given above, are so similar to those that 

 follow^them, that Groups I and II of Table VIII can be com- 

 bined, with a bracket. In this rearrangement. Groups III 

 and IV remain unchanged. The grouping now corresponds 

 quite closely to that previously adopted for the Bull-frog. 



When the weight of the muscles of the thigh is compared 



with that of the muscles of the remainder of the leg, the ratios 



are nearly constant, as is shown in Table IX, 



TABLE IX. 



Ratio of the weight of the To weight of muscles of 

 Group. muscles of the thigh the remainder of the leg. 



When we compare these ratios for virescens with those for 

 the Bull-frog, we find first that, while the absolute value is 1.85 

 or more for the Bull-frog, it is only 1.80 or less for virescens. 



In proportion to the rest of the leg the muscles of the 

 thigh are therefore slightly less well developed in virescens. 



The records for the two species agree nevertheless, in the 

 fact that the proportional weight of the thigh muscles is greater 

 in the group of lightest specimens than in the group of heaviest. 

 The difference is however slight. 



XII. Length of leg bones. 



Still maintaining the grouping last employed, we may com- 

 pare the length of all the bones of the leg taken together with 



