334 



The reciprocal multiplied by the total miles gives velocity in miles per 

 hour. The reciprocals of the time to complete any unit of work are thus 

 a convenient expression of relative velocity. 



The activity of cold-blooded animals, such as insects and millipeds, in 

 a general way varies directly with temperature just as development does. 

 Also, rate of progression may be used as an index of physiological activity, 

 and something of the laws governing rate of development may be ascer- 

 tained from a study of progression. 



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16 23 iO 32 54 3tf 



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Fig. 2. Rate of creeping of a diplopod at various temperatures, shown in 

 millimeters per minute and in progression units (41.44 mm) per minute. Note 

 how the velocity curve CD departs from a straight line above 2S° C. and below 

 22° C; and how the time-temperature curve AB differs from an equilateral 

 hyperbola. (Date from Crozier '24.) 



Fig. 2 shows a curve for the velocity of progression, or rate of creep- 

 ing, of a milliped, plotted from the experimental data of Crozier ('24) . For 

 velocities of progression of 500 — 750 mm. per minute (temperatures 

 22° — 28° C), a milliped in an experiment conducted at a temperature 

 one degree higher than 22° adds il.-l-i mm. to the distance traveled in one 

 minute. Likewise, an animal in an experiment at two degrees higher than 



