BT D. EMBLETOlN^, M.D. 63 



especially whilst it is being expelled through the sphincters, and 

 that the amount of such pain and inconvenience will greatly vary 

 among the various tribes of the feathered race. 



No one who has examined with attention and compared the 

 parts concerned in their quiescent, unimpregnated, and in their 

 active breeding conditions, can view without surprise and admi- 

 ration the vast change that they have undergone in passing from 

 one to the other state ; and no one can wonder that pain should 

 be the consequence of such extreme distension of the oviduct as 

 takes place in birds, particularly in those which lay eggs large 

 in proportion to their bodies. It would be a marvel if in such 

 cases during parturition no blood were shed. 



lY. With regard to the form of eggs, we know that it varies 

 greatly, from the rounded, more or or less globular shape of those 

 of some of the Falconidse and Strigidae, some of the Willow Wrens 

 and of the Ostrich and Cassowary, to the extremely pyriform con- 

 dition of those of the Waders and Guillemots, and the long oval, 

 spindle form of those of Cormorants, Gannets, and Grebes; the 

 eggs of the Common Powl, and many others, usually exhibiting a 

 beautiful intermediate ovoid. See Plates I. -IV. 



Ko doubt can exist that all the forms of eggs are produced by 

 the varied actions of the longitudinal and circular muscular layers 

 in the wall of the oviduct. These layers, like their analogues 

 in the wall of the intestine, arc, to a certain extent, and under 

 certain circumstances, mutually antagonistic, whilst under other 

 conditions they aid each other. They can restrain or expedite the 

 passage of the egg, their normally combined and regulated efforts 

 resulting in its final, orderly passage ; just as those of the mus- 

 cular layers of the intestine result in the transit of the fieces 

 which, in many animals, are rounded or ovoid. 



The form of the egg must be impressed upon it before it reaches 

 the isthmus, or at least on its arrival at that part of the oviduct. 



In the case of a rounded egg the propelling and tlie restrain- 

 ing forces must be nearly balanced, but there ought to be a 

 preponderance on the side of the former ; for if they were 

 equal, the egg would, in all probability, become stationary 



