PROCESS OF CLEAVAGE IN BATRACHIAN OVA. 511 



by the separation of the formed elements from one another, 

 and not by an inversion. Proceeding from this groove, I also 

 saw in transverse sections a trace of a division (Trennungs-spur) 

 in one of the mantle surfaces extending upwards in a direction 

 not quite parallel to the dorsal half. I therefore believe I am 

 justified in considering this trace of division as the rudiment 

 of the Rusconian cavity, and in maintaining that this arises 

 not by an inversion, but by a separation of the morphological 

 elements from one another. 



In regard to the question whether inversion or fission occurs, 

 Golubew, who is the only author besides myself that has 

 expressed himself definitely upon the point, is in favour of my 

 view. Golubew* however states that my account of the mode 

 of origin of the Rusconian cavity is not quite accurate. I 

 cannot here enter into a controversy upon the subject, because, 

 faithful to my project, I can only so far consider the anatomical 

 details as may be necessary to render the formation of the 

 layers intelligible. In regard to the relations of the fissure 'to 

 the embryonic laminae there are no differences of opinion. 



Remak noticed that a group of white germ cells projects 

 from the floor of the cleavage cavity, just at the margin where 

 this is continuous with the roof of the cavity, for some distance 

 towards the roof (z, fig. 399). If have further pointed out that 

 this projecting mass of cells is of fundamental importance in 

 the formation of the laminae. 



I have shown that the roof of the cleavage cavity (D, fig. 

 399) contains the rudiment of the sensorial lamina of Remak 

 alone,* and that the analogues of those laminae termed by 

 Remak the middle and gland laminae, are formed from the cells 

 that are applied as new formations to the roof. 



When I found that these germ cells reached at first only a 

 small distance towards the dorsal half, whilst they subsequently 

 extended more and more, until they at length passed beyond the 

 upper pole, the germ cells of the abdominal half at the same time 

 similarly stretching upwards to the roof, and growing towards 



* Loc. cit., Taf. D, fig. 2. 

 f Loc. cit. 



J The same fact has been subsequently pointed out by Gotte. See Max 

 Schultze's Archiv, Band iv. 



