SECT, i] THE UNFERTILISED EGG 233 



enumerated the parts of the typical avian ovum. Fig. 13, however, 

 shows the general disposition of parts diagrammatically. 



First, as to size and shape. The size and shape of the egg were shown 

 by Curtis in 191 1 and by Surface in 191 2 to be due partly to the 

 structure of the oviduct, which very probably may be considered an 

 inherited character, as was claimed by Newton. D'Arcy Thompson's 

 discussion of the mechanics of egg-formation in birds, in his Growth 



" White or Milky Yolk 



\ Germinal Di^c .Pander's Nucleus 

 Shell -Membranes ^ ^ ' t- _ , ^ 



Shell 



Latebra 



Chalazae ^^^^^^'^ ' "^ ...^'^ ^ 



(Treadles, HailstOTie^r^^^::;^^^ I ^ ^^^^^^'^ ^, \ 



y, ^^=^^^^^ — 1-______-^ ^^^^'^ Chalazae 



/■ «r~ I ^; ^ 



Vitelline Membmne Haloes or ^ 



Layers of Yellow Yolk ^Whi te 



Fig. 13. Diagrammatic representation of the hen's egg. The chalazae were called by 

 Tredern Ligamenta albuminis. Bartelmez gives a discussion of the factors governing 

 the angle which the embryonic axis makes with the axis of the egg as a whole. The 

 yolk is not a perfect sphere but lengthened along the main axis. The egg-white 

 is divisible into three layers which increase in density from without inwards. The 

 chalazae, as Berthold was the first to find, are not present in reptilian eggs. 



and Form, will be famiHar, but some biologists, such as Horwood, 

 have taken exception to his conclusions about the physical influences 

 which shape the egg. Ernst's well-known experiment was the starting- 

 point of these discussions ; she caused hens to lay on a surface of wet 

 sand and charcoal, and so, observing the process, found the blunt end 

 to be blackened. This was in agreement with many other observers, 

 such as V. Nathusius; Landois; Jasse; Konig-Warthausen and Erd- 

 mann; and d'Arcy Thompson accordingly described the hen's egg 

 as moving down the oviduct blunt end forwards, the pointed end 

 owing its form to the peristaltic compression of the oviduct. Unfor- 



