GERMINAL MEMBRANE. 53 



applied to a drop of the contents of the egg, it does not appear 

 to act materially upon the cells, and the contained corpuscle 

 becomes paler and somewhat swollen, which could not well 

 take place if it were fat. These cells, then, arc the earlier 

 stage of development of the subsequent globules of the yelk- 

 cavity. The larger ones already resemble them perfectly. 

 These globules of the yelk-cavity are therefore likewise cells. 

 Their nucleus-globule (Kernkugel) is acted on by acetic acid 

 precisely in the same way as it was in the earlier condition. 

 It does not lie centrally in the cell, but on the internal surface 

 of the wall, as is seen when the cells are caused to roll under 

 the microscope. When at rest, however, they are generally so 

 placed that the nucleus-globule occupies the most depending 

 point (because probably it is the heaviest portion of the cell), and, 

 on that account, it then appears to lie in the centre of the cell. 

 The yelk in the first instance contains only the yelk-cavity, 

 with its cells ; the proper yelk-substance with its globules not 

 being as yet formed. The colour of these young eggs is there- 

 fore also white, like the contents of the yelk-cavity. 



The membrane-like layer which surrounds the above-described 

 contents of the egg, may be completely separated from the parts 

 which surround it externally with facility, after the egg has 

 been divided through the centre. It is not connected with 

 them, and appears, to the unaided eye at least, to be pretty 

 smooth on its external surface ; it is not possible to trace it 

 towards the interior. Its structure is peculiar. Purkinje, who 

 discovered it, describes it as consisting of globules, which re- 

 semble in form and size, but are more transparent than the 

 blood.-corpuscles. When spread out upon a plate of glass, and 

 examined with the microscope, it is seen to consist of two parts, 

 an internal minutely granulous stratum, and an external layer 

 of cells. Numerous little granules are observed in the internal 

 stratum, which resemble the nuclei of the above-described cells 

 of the yelk-cavity in their earliest stage, and I conjecture that 

 the cells of the yelk-cavity are formed from this stratum, so 

 that in fact it still pertains to the yelk-cavity. The external 

 layer consists of small round granulous cells, each of which 

 contains a nucleus, which again in many instances encloses 

 one or two nucleoli. Two or three such lavers of cells lie one 

 above another. These layers of cells are surrounded externally 



