( 365 ) 



the number of chromosomes was again doubled in the ovum, which 

 now awaited fertilisation in the venter; the latter already communi- 

 cated with the exterior. 



These two discoveries seem to us to justify the conclusion that 

 before fertilisation the ovum contains six chromosomes. 



We next had to attempt to find how there could be again twelve 

 chromosomes after fertilisation. There were six chromosomes in the 

 ovum and three in the spermatozoid. If fecundation were to take 

 place in the ordinary manner, there would still only be nine chromo- 

 somes, whereas the sporogonia have twelve. 



For this purpose we fixed and cut several hundred female plants 

 of Polytrichum. There was of course only a small chance, that a 

 given plant would contain a fertilized archegonium, fixed at the right 

 moment. In a number of cases we found, however, the desired stages 

 and so now possess a fine series of preparations, illustrating in regular 

 succession, the fertilisation process from the penetration and modi- 

 fication of the spermatozoid onwards. 



The number of spermatozoids which enter the venter of the arche- 

 gonium is sometimes very great, but after some have penetrated into 

 the ovum, the others no longer closely surround the ovum, but lie 

 more in the direction of the neck. Hence it would appear that here 

 also the fertilized egg exerts a repulsive action. 



The youngest stage, which we now possess, and which lias been 

 observed several times, shows near the periphery, but without a 

 doubt imbedded in the cytoplasm of the ovum, two spermatozoids; 

 their length, their shape, everything agrees with that view. 



In a later stage both are in contact with the nucleus; they have 

 become thicker and shorter. This thickening and shortening proceeds 

 until there are two oblong corpuscles, containing a few dark granules 

 in their interior, and lying against the nucleus. 



We also found a few examples of the next stage, namely an ovum 

 which clearly showed three nuclei, each with a thick mass of chro- 

 matin, and another ovum, in which the demarcation between the 

 three nuclei was no longer so obvious; the circumference of the 

 nucleus in the latter case was, however, still indented and inside the 

 nucleus there were three dark masses of chromatin. We find there- 

 fore, that the cells of the sporophyte contain twelve chromosomes, 

 that those of the gametophyte have six, and that the spermatozoids 

 have three. The ovum has again six chromosomes after fusion with 

 the ventral canal-cell, and after fecundation by two spermatozoids 

 there are once more twelve chromosomes. 



