68 Translation from Purkinje 



it, is so similar in form to the cicatricula that it is no wonder that for 

 some time an absurd opinion confused the one with the other, espe- 

 cially since in the hard-boiled egg the albuminous cicatricula could 

 hardly be distinguished from the albumen to which it adheres. 



The white substance contained in the central latebra of the yolk, 

 as seen under the microscope, consists of rather large white globules 

 suspended in an albumen. It has almost the same consistency and 

 structure as that which makes up the fluid part of the cicatricula, 

 so it would seem that there is some developmental relationship be- 

 tween the two regions. The rest of the latebra is filled with a rather 

 fluid lymph. It is more convenient to look for this structure of the 

 yolk in boiled eggs, so long as you are sure that it was not produced 

 [; 8 ] in the first place by the cooking. At times between the first and middle 

 strata [of yolk] I have found a spherical lamella of coagulated albu- 

 men, or here and there albuminous projections from the center, espe- 

 cially in eggs that had already been incubated for some hours. In the 

 boiled yolk it appears that the central latebra often presents an irregu- 

 lar figure and at the same time the concentric strata have correspond- 

 ing irregularities. In the boiled yolks the central latebra contains a 

 milky substance somewhat salty in flavor so that from this it is clear 

 that it differs chemically from the rest of the yolk. In many eggs I 

 have found the inner layer of yolk rather oily, translucent and deep 

 yellow, but I have not yet discovered on what conditions this de- 

 pends. What further changes the yolk may undergo during incuba- 

 tion, how the halos around the cicatricula are produced in it, how the 

 albumen is gradually mixed with it, must remain for later investiga- 

 tions. For the sake of those who enjoy microscopic observation, I may 

 add that the boiled yolk, which readily disintegrates into a powder, 

 shows masses of the most beautiful corpuscles, simulating crystals in 

 form, and indeed those removed from different parts of the yolk show 

 different patterns. 



§6 



Concerning the vitelline membrane. 



The vitelline membrane is uniformly delicate and exceedingly 

 transparent and shows no organic structure under the microscope, 

 no matter how it is cut up or teased. It is a perfectly intact closed 

 vesicle, pierced by no opening. In the ovarian ovule, to be sure, you 

 can scarcely differentiate it in early stages from the layers of globules 

 which are laid down by the yolk peripherally; at that time also the 

 vesicle of the cicatricula is so joined to it that it is not possible to 

 separate one from the other without injury. Even in older ova, the 

 membrane of the germinal vesicle sticks so fast to the vitelline mem- 

 brane that very often in separating them you tear the latter, leaving 



