494 



ON INCREASE IN SIZE 



[PT. Ill 



shortest known), M, bonariensis, less parasitic, takes 11-5, and M. 

 rufo-axillaris , still less so, takes 12-5 to 13 days. 



No consideration of the questions involved in incubation and 

 gestation time would be complete without mention of the work of 

 Rubner. Rubner found that, if a graph is constructed having the 

 durations of pregnancy of different groups of animals as abscissae 

 and the respective birth-weights of their young as ordinates, the 

 resulting curve is quite smooth and regular. These facts, which have 

 already been discussed, are shown in Fig. 75, taken from Rubner. 

 A glance shows that the only exception among the animals which 

 Rubner chose is man, who develops very slowly, and does not attain 

 at birth more than a quarter of the weight he should if he resembled 

 other animals. Rubner considered the anthropoid apes to be more 

 like animals than man in this matter, but an observation of Heinroth's 

 makes this doubtful. It has often been pointed out that small 

 birth-weight is probably an adaptive feature of considerable ad- 

 vantage to the human female. The actual figures are as follows : 



Table 67. 



Average 



7-6 



Rubner studied the heat production of the new-born animals, and 

 found that the larger the birth-weight the smaller the number of 

 Calories put out by i kilo of body-weight per day. Thus for a new- 

 born animal weighing 50 kilos, i kilo of body- weight would produce 

 34*2 Calories, for one weighing 25 kilos the production would be 

 42-6 Calories, for one of 12-5 kilos it was 60 Calories, and for one 

 of 6-25 kilos it was 66-6 Calories. The explanation of this obviously 

 was that, since no supply of energy can be built up in toto into 



