4 8 



FRANK R. LILLIE. 



deepens gradually into a canal that penetrates into a mass of 

 mesoblast connected with the somatopleure, and excavates a large 

 irregular cavity in this. The mass extends forwards to the tip of 

 the ventricle and ends in a bifurcated extremity. This represents 

 the allantois. the main mass of which is composed of loose, very 

 vascular mesenchyme forming an appendage to the somatopleure 

 on the left side. On the right side the mesoblast of the somato- 

 pleure in the allantoic region is much hypertrophied and forms a 

 large free lobe without any entodermal contents. 



It is remarkable that the allantoic rudiments should show such 

 considerable power of growth in the absence of the usual stimulus 

 of internal pressure, which is precluded by the open groove-like 

 connection with the intestine. 



Experiment 24.. 



The hind end of an embryo was cauterized with the aim of 

 destroying the incipient tail-bud and the region of the hind- 



FIG. 8. Defective embryo (Experiment 24). 



limbs. The egg was reopened 48 hours after the operation. The 

 vascular area covered about two fifths of the yolk, and appeared 

 to be entirely normal. 



