ON THE ORIGIN OF DI >l MLE-YOLKKD EGGS. 185 



indicates that the conditions followed by increased permeability 

 are to be looked for in the egg. If ova in the same state have an 

 identical blood supply they will undergo equivalent growth, but 

 mere identity in their circulation does not insure this. 



Although these considerations are necessarily speculative, their 

 possible relation to more remote matters may be briefly men- 

 tioned. It is certainly a remarkable fact that in the human 

 ovary, to mention a case among mammals, and in the hen's 

 ovary, to mention one among birds, normally one egg ripens after 

 another, whereas in the ovaries of amphibians and fishes thou- 

 sands of eggs may ripen at one time. It is quite possible that 

 the conditions which in the one case lead to an abnormality are 

 identical with those which in the other give a typical result. 

 In no case do all the eggs contained in any of these ovaries ripen 

 at the same time. This certainly points to alterations in the 

 permeability of the ovum as a factor in the initiation of its 

 growth period, and suggests that these changes are directly 

 traceable to the activity of the egg. The fusion of normally 

 distinct follicles in the hen's ovary brings about secondarily an 

 identical vascularization and thus accidentally duplicates the 

 nutritive conditions prevalent in the ovaries of certain other 

 forms. 



Identity of blood supply then is suggested as an explanation 

 of the synchronic yolk formation in these eggs, whereas a change 

 in permeability undergone independently on the part of the 

 eggs themselves introduces this period of growth. This change 

 in permeability must necessarily also be synchronic if double- 

 yolked eggs are to be produced, but how this synchronism is 

 brought about in certain eggs, and how it is prevented in others, 

 cannot be profitably discussed in our present state of knowledge. 



The important thing after all is that a bird's ovary, with 

 follicles secondarily fused as described in the preceding pages, 

 does actually give rise to a series of double-yolked eggs, and this 

 remains true even if my suggestions as to the development and 

 physiology of this organ should prove to be entirely wrong. It 

 is to be hoped that the clinical symptoms given may aid in the 

 discovery of further material upon which more detailed studies 

 in the living state could be carried out with great advantage to 



