938 ON THE SHAPES OF EGGS [ch. 



waves of contraction. These muscular contractions hiay be de- 

 scribed as the contraction of successive annuli of muscle, giving 

 annular (or radial) pressure to successive portions of the egg ; they 

 drive the egg forward against the frictional resistance of the tube, 

 while tending at the same time to distort its form. While nothing 

 is known, so far as I am aware, of the muscular physiology of the 

 oviduct, it is well known in the case of the intestine that the presence 

 of an obstruction leads to the development of violent contractions 

 in its rear, which waves of contraction die away, and are scarcely 

 if at all propagated in advance of the obstruction ; indeed in normal 

 intestinal peristalsis a wave of relaxation travels close ahead of the 

 wave of constriction. 



(4) The egg is, to all intents and purposes, a solid of revolution ; 

 in other words, its transverse sections are all but perfect circles, 

 sd nearly perfect that, chucked in the lathe, an egg "runs true." 

 This may be taken to shew that the direct pressure of the oviduct, 

 whether elastic or muscular,* is large compared with the weight of 

 the egg. Even in ostrich eggs, where if anywhere gravitational 

 deformation should be found, the greatest and least equatorial 

 diameters do not differ by 1 per cent., and sometimes by less than 

 one part in a thousand*. 



(5) It is known by observation that a hen's egg is always laid 

 blunt end foremost f. 



(6) It can be shewn, at least as a very common rule, that those 

 eggs which are most unsjnnmetrical, or most tapered off posteriorly, 

 are also eggs of a large size relatively to the parent bird. The 

 guillemot is a notable case in point, and so also are the curlews, 

 sandpipers, phaleropes and terns. We may accordingly presume 

 that the more pointed eggs are those that are large relatively to 

 the tube or oviduct through which they have to pass, or, in other 

 words, are those which are subject to the greatest pressure while 



* Cf. Mailock, op. cit. 



t This was known to Albertus Magnus, though his explanation was wrong, 

 "Ova autem habentia duos colores non sunt oranino penitus rotunda, sed ex una 

 parte sunt acuta habentia angulum sphericum acutum, sicut sunt composita ex 

 duobus seraispheris, in una parte extensis ad angulum acutum et in alia parte 

 sphericis noo extensis in loco ubi est polus ovi. . . . Et in exitu ovi acutus angulus 

 exit uliimo, eo quod ipse porrectus est ad interiora matricis versus parietem ubi 

 ovum cum matrice continuatur in sui generatione" {De animalibas, lib. xvii, 

 tract. 1, c. 3). 



