512 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



them ; and after I* had further discovered that the cells of the 

 Batrachian germ were capable of spontaneously changing their 

 form and position on the slide, I stated my opinion that these 

 germ cells strove to pass outwards by spontaneous movements, 

 in opposition to the laws of gravity. Golubewf is unable to 

 adopt this view. He believes that the increase in height is 

 due to cleavage processes. 



I am again unable to enter into any discussion in this place 

 upon the different opinions we hold. The question whether 

 the cells move from their position spontaneously, or as the 

 result of progressive fission, is of interest in and by itself, but is 

 of quite secondary importance in regard to the development of 

 the laminae. It is here only important to notice that the cells 

 generally suffer displacement in order to aid the formation 

 of the embryonal laminae ; and this circumstance may again be 

 regarded as admitted on all sides. 



It has been already pointed out that the fissure proceeding 

 from the dorsally situated furrow of Rusconi runs upwards. 



When the semilunar fissure in the course of its upward ex- 

 tension reaches the margin of the cleavage cavity, it meets with 

 the above-mentioned white germ cells, which extend along the 

 dorsal half from the floor of the cleavage cavity to the roof. 

 The fissure penetrates these upward extending cells. 



If numerous horizontal sections, beginning from the inferior 

 pole, are carried through the ovum, it is found that the fissure 

 existing in the dorsal half is almost semilunar. It is bounded 

 externally by the mantle layer composed of small cells, and 

 internally by the white germ cells (z). The mantle zone is 

 at this point much thicker than where it forms the roof 

 of the cleavage cavity. In other words, the. fission of the large 

 germ cells to form small ones has at this point progressed 

 towards the axis of the ovum. That which now lies on the 

 exterior of the fissure is no longer the analogue of the senso- 

 rial lamina (Remak), but contains the rudiments of all the 

 germ-laminae. From the fissure a part of the visceral cavity is 

 subsequently formed, and that which lies more externally forms 



* Ueber die selbstdndigen Beivegungen, etc. , Wiener Sitzungsberichte, 1863. 

 t Loc. cit. 



