Ryder.] ^^8 [^prji 2], 



kinetogeiietic factor in the development of the shells of eggs is proved by 

 the fact that the latter vary in form very widely. So much is this the 

 case that a distinctly different algebraic formula would have to be worked 

 out for every variation of the form and size of eggs laid by even the same 

 bird. If the very slight disturbances of the counterpoise of the energies 

 on either side of the axis y which condition and determine the figure of 

 such a body as a hen's egg are sufficient to produce the remarkable vari- 

 ations which we may see by the thousand in any marketplace, how slight 

 must be the disturbances of the interplay of the living energies tliat need 

 to be set up in living bodies in order to produce the endless number of 

 variations that they present. If the figure of the hen's egg is dependent 

 upon the mode and condition of the equilibration of forces developed 

 within an oviduct, what reason is there to doubt that plastic organisms 

 are so modified, only in ways a thousand times more complex and difficult 

 to unravel and explain. 



The application of the principle here developed is very extensive. It 

 applies also to an evplanation of the oval and ovoidal forms of the eggs 

 of many animals that are manifestly due to causes operating in much the 

 same way. Those of many insects at once occur as a case in point. The 

 elongated blastocysts of mammals growing under a condition of annular 

 constraint within a tubular uterus or uterine tubule are other cases that 

 illustrate the same doctrine. The foregoing discussion also clearly ex- 

 plains why it is that the blunt end of the hen's egg comes down the ovi- 

 duct as its foremost portion and not the sharp end, as one would be led to 

 suppose, were it not positively established that such is not the case.* It also 

 makes it evident that variations in the figure of the eggs of birds are due 

 to the exhibition of varying quantities of energy and to different condi- 

 tions of activity of the walls of the oviduct during the formation of the 

 secondary egg envelopes, in the thus protracted process of oviposition. 



One may be further permitted to surmise that in its nearly completed 

 state in the oviduct that the prolonged and at first voluntary retention of 

 the egg in the latter by the parent distinctly tended to cause the deposit of 

 the third and last homogeneous matrix into which calcareous infiltration 

 occurred automatically as suggested above. The retention of the egg in 

 the oviduct caused it to act as an irritant when a second and last basement 

 membrane, the matrix of the future shell, was thrown down in the ovi- 

 duct comparable to that of the basement membrane or zona deposited 

 around the ovum as the vitelline membrane in the ovarian follicle. Tlie 

 evolution of the eggshell itself may, therefore, with the utmost show of prob- 

 ability, be traced to a voluntary and more or less intelligent desire of the 

 female parent to protect its potential ofispring for a time within her own 

 body. In carrying out this protective instinct which preceded the habit 

 of nest-building, concealment or burial of the whole laying was resorted 

 to, as still practiced by reptiles, such as alligators and turtles. The entire 

 brood or nestful were also at first laid at once and concealed, and a 



* The evidence for tins was first adduced by Nathiisius, Zoolog. Anzcigcr, Vol. viii. 



