376 



ON INCREASE IN SIZE 



[PT. Ill 



Ibsen, and Ibsen & Ibsen, Draper's figures form the standard series, 

 and are shown in Tables 6 and 7 of Appendix i. As is generally 

 known, the guinea-pig differs from most other mammals in being 

 born much later in its life-span than is usual, so that its lactation 

 period is exceedingly short and it is able to eat green food a very 

 few days after its birth. This is reflected in its gestation time which 

 is relatively long. 



15 



20 



25 



30 



35 40 

 Fig. 26. 



45 



50 



55 



60 65 



During the 64 days of its development in utero, the guinea-pig 

 increases its weight to about 85 gm. and its length to 10 cm. This 

 process is shown in Fig. 25 taken from the figures of Draper. In 

 Fig. 26, which gives an enlarged view of the lower part of the growth- 

 curve, the increase in weight of the placenta, the membranes, and 

 adnexa, together with the amniotic and allantoic fluid, is also shown. 

 The extra-embryonic structures reach a more or less constant weight 

 about two-thirds of the way through development, but, as can be 

 seen from Table 5 of Appendix i, the values from which this curve 

 was drawn are very divergent. In comparing the growth of the 



