THE OVUM. 



95 



boiled, but it is transformed in the process of hatching into a mass like the albumin 

 in the eggs of nonnesting birds (hen). On the other hand, the albumin of hen's eggs 

 coagulates on addition of dilute sodium hydroxid into a vitreous transparent mass. 



Germinal vesicle and spot. 



Blastoderm 



Its processes. 



L Marginal 

 protoplasm. 



FIG. 359. Diagrammatic Representation of a Mesoblastic Ovum 

 (after Waldeyer). 



FIG. 360. a White, b 

 yellow yolk-globules. 



Ch.l. 



i.s.iri. 

 a.c.h. 



The fibers of the membrana testacea are secreted, spontaneously coagulated 

 keratin-like filaments, wound spirally about the albumin, upon which a 

 porous cement (testa) consisting of a mixture of albumin and lime is deposited 

 in the lower portion of the oviduct. A structureless, porous, mucinous, occasion- 

 ally fatty cuticula repre- 

 sents the outermost 

 shell-layer in some birds. 

 The limeshell of the 

 bird's egg is utilized in 

 part for the formation 

 of the bones of the chick. 

 The coloring-matters of 

 the surface of the egg, 

 which are often present 

 in several superposed 

 layers, appear to be 

 derivatives of hemoglo- 

 bin (hematoporphyrin) 

 and biliverdin. Between 

 the albumin and the 

 shell-membrane there is 

 detached epithelium of 

 the oviduct (Fig. 361). 



The white yolk (hen) 

 contains albumin, nu- 

 clein , lecithin , potassium , 

 glycogen (?); the yolk- 

 membrane keratin. The 

 yellow yolk contains a 

 nuclein containing iron, 

 a vitellin resembling 

 globulin, lecithin, cho- 

 lesterin, fat, coloring- 

 matters ( iron - lutein ) , 

 containing neuridin, glu- 

 cose, mineral matters, 

 cerebrin (?), amyloid granules (?), sodium, potassium, calcium, magnesium, iron, 

 phosphoric acid, silicic acid. The white of egg contains crystallizable ovalbumin 

 (a mixture of several albumins), together with globulin, a body resembling mucin, 

 sugar and keratin. The ash contains more chlorin and alkalies, but less calcium, 

 phosphoric acid and iron than the yolk. 



s.m. 



x ch.l. 



x. 



FIG. 361. Diagrammatic Longitudinal Section of a Hen's Egg: b.l., 

 germinal layer (cicatricula) ; w.y., latebra, filled with white yolk; y.y., 

 y.y., a number of layers of yellow yolk, surrounding the latebra concen- 

 trically; x, yolk-membrane; v.t., white yolk-cortex (cortical proto- 

 plasm); w, mass of surrounding albumin in layers; ch.l., chalazar, 

 a.c.h., air-chamber at the blunt pole of the egg; i.s.m. internal and 

 s.m. external lamella of the shell-membrane (membrana testacea); s, 

 lime-shell (testa). 



