35^ Raymond Pearl 



no doubt that had the observations been extended to lOO eggs 

 these "down" fluctuations would have been offset by an "up" 

 set, and the theoretical curve would have shown no downward 

 tendency at its upper end. This is indeed directly indicated in 

 the value of the 87th observation. This egg had the highest index 

 of any ever laid by hen No. 183. If the observations had been 

 stopped at 60 eggs the theoretical curve again would not have 

 shown the slight downward tendency at the upper end. That it 

 does show this is simply an accident resulting from ending the 

 observations at a particular point. 



DISCUSSION OF RESULTS 



The facts which have been set forth above are of interest in 

 connection with two questions, viz: (i) the physiology of the deter- 

 mination of the shape of the egg and (2) the more general ques- 

 tion of regulation in morphogenesis. 



With regard to the first of these questions there are two features 

 of the present case which lend strong support to the view that 

 the shape of the egg is determined by the active contractions of the 

 muscular wall of the uterus. (Cf. p. 6 supra, and Szielasko ('05) 

 p. 289.) These features are: {a) that the eggs laid by this hen 

 were not all alike or even approximately alike. There were great 

 differences in the shape of different eggs, {h) That the shape of 

 the eggs changed in an orderly and progressive fashion (regulation) 

 as they were successively laid. It is hardly conceivable that these 

 two things both could have occurred with the uterus playing sim- 

 ply a passive part and only influencing the shape of the egg through 

 the elasticity of its walls. It might possibly be maintained that 

 the uterus wall became more and more stretched peripherally 

 as more eggs were laid, and that this would account for the thick- 

 ening and rounding up of the egg in a purely passive way. But 

 if this position is taken one is at a loss to explain the sudden occur- 

 rence of a relatively long narrow egg in the middle of a whole 

 series of approximately normal ones. An example of such occur- 

 rence is given by egg No. 36, and another by egg No. 62. 



The only reasonable conclusion on this point appears to be that 



