32 M. Pli. Owsjannikow on the 



capable of being fertilized and in all the protoplasmic protu- 

 berance was noticeable directly after the act of fertilization. 



In order that the several portions of the embryo shall be 

 more readily distinguishable from one another, it is necessary 

 for the preparations to be thoroughly stained. The prevalent 

 idea that the egg-membrane is impervious to stains is erro- 

 neous. I found that several staining-fluids penetrate the 

 ovum and the embryo. The ova took the best stain, no 

 matter whether at first treated with Flemming's fluid, alcohol, 

 or osmic acid, by being immersed for from twelve to four- 

 and-twenty hours in a strong saturated solution of hsema- 

 toxylin. A longer immersion causes the yolk-granules to 

 become coal-black. 



I possess a large series of sections in which there may be 

 seen all those processes which set in immediately after fertili- 

 zation, and were observed and described in living ova by 

 A. Miiller, Kupffer, Benecke, Calberla, and myself. 



By treatment with osmic acid the contents of the ovum 

 are instantaneously hardened, so that in sections we are 

 enabled to get a good view of the protuberance which arises 

 at fertilization as well as the protoplasm, which usually 

 appears on the withdrawal of the yolk from the egg- 

 membrane. 



Moreover, in the serial sections we may study the most 

 varied forms of mitoses, which appear at the division of the 

 nucleus before the formation of the new yolk-segments. 



The time occupied by the various metamorphoses in the 

 ovum depends upon the temperature at which the fertilized 

 ova are kept. This fact explains why the divisions of the 

 yolk which I previously described in the ova of the lamprey 

 proceeded more rapidly than they were found to do by Cal- 

 berla. Kupffer states that at Konigsberg, when the tempe- 

 rature of the air stood at from 8° to 10° C. (46°'4 to 50° F.), 

 the larvae were hatched on the sixteentli or seventeenth day, 

 and at Naples at the end of the eighth day. My larvae 

 hatched out on the ninth or tenth day at an atmospheric 

 temperature of about 16° K. (68° F.). 



The first furrow is a longitudinal one, which consequently 

 has a meridional direction and divides the yolk into two 

 perfectly equal portions. 



The furrow begins from the nucleus, which for a long time 

 lies almost entirely superficially in the neighboui'hood of the 

 active pole. 



The first segmentation proceeds exceedingly slowly. We 

 observe long fibres radiating from the nucleus, which are 



