374 



ON INCREASE IN SIZE 



[PT. Ill 



photograph of a model of the oviduct with its contained eggs. By 

 reconstruction methods at a magnification of looo diameters of the 

 ova Huber was able to determine the volume changes during seg- 

 mentation as follows: 



Age 



There would, therefore, appear to be a certain increase in volume 

 during these very early stages, but as the specific gravity changes 

 are not known it is difficult to understand what it may imply. There 

 is at present a great gap in our knowledge of the embryonic growth 



Fig. 24. 



of the rat between the early point at which Ruber's studies end and 

 the later one at which those of Stotsenberg begin. Huber himself 

 suggested that the slow development of the ovum of the rat during 

 its passage down the oviduct was best accounted for by the lack of 

 any food-supply for an alecithic egg until fixation to the uterine wall 

 had taken place. As the whole embryonic period of the rat is only 

 22 days, it is of great interest that the first four days should involve 

 hardly any increase in size. This fact renders of no significance the 

 calculated weights of rat foetuses given by Donaldson, Dunn & 



