. Chemical embryology. Embryology. 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 1911 and by Surface in 1912 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 -Memb
. Chemical embryology. Embryology. 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 1911 and by Surface in 1912 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, ^^=^^^^^â1-______-^^^^^'^ Chalazae /â «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-.
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Keywords: ., bookcentury1900, bookpublishernewyorkthem, booksubjectembryology
