66 Translation from Purkinje 



the passage in Tiedemann* where he says that the cicatricula is com- 

 parable to the Graafian ovules in mammals, because it is the first struc- 

 ture to develop in the ovule and that it has the form of a compressed 

 vesicle or white spot. It is certainly not difficult to remove this vesicle 

 of ours in small eggs where it is not yet surrounded by white globular 

 material; in mature ova this is a more difficult undertaking. The fol- 

 lowing method, which I hit upon by chance at first, was of the greatest 

 help to me later. After you have very carefully separated the cumulus 

 with its porus from the vitelline membrane under water, using a 

 probe or curved needle, allow it to settle to the bottom of a dish which 

 must have a convex bottom; then as the water is pipetted off, the 

 cumulus will spread and the vesicle will stand revealed, if not at first, 

 [^6] at least after several trials. But you must be exceedingly careful lest 

 you suck up the specimen with the water and destroy it. Indeed, the 

 consistency of the vesicle is so delicate that in the smaller eggs it may 

 burst like a water bubble at the slightest touch. 



§4 



The vesicle of the cicatricula as a 



normal female organ in birds. 



In reflecting on the significance of our vesicle, the first thought that 

 arose was that it might be a sign of mating and that it would not be 

 found in the ovules of hens which had not been kept with the cock."' 

 However, it was also found in isolated hens, all of wdiose eggs were 

 examined to make sure, and found to be infertile. In some it seemed 

 to me more delicate and much more difficult to isolate; in others abso- 

 lutely no distinction was found. 



§5 



Concerning the development of the 



yolk and its central latebra. 



With regard to the development of the yolk, I find only a few things 

 to be noted. At the beginning, clear miliary vesicles can be observed 

 projecting out in great numbers from the ovarian surface like a skin 

 eruption. At this time the yolk is a clear fluid material not easily 

 differentiated from the vesicle of the cicatricula. By the time the ovule 

 has attained the diameter of one line, the whitish yolk becomes turbid 

 and the vesicle appears transparent through the external membranes. 

 \Vhen it has reached the size of a pea, the yolk has taken on the color 

 of thick yellowish milk. Then oily droplets can be recognized, though 



* Zoologie, Vol. Ill, p. loo. [Friedrich Tiedemann (1781-1861). His text was pub- 

 lished in 3 volumes between 1808 and 1814. Vol. Ill has the subtitle Anatomie und 

 Naturgeschichte der Vogel.] 



