424 Dr. A. Borgert on the Reproduction 



globules^ and take a deep stain with safranine ; these threads 

 consequently exhibit the property of chromatin." 



The sections that I have prepared have led me to a different 

 interpretation, according to which the plates consist of nume- 

 rous segments of unequal length lying very close together. 

 The iinger-shaped outgrowths of a relatively feebly stainable 

 substance, which Karawaiew describes, can only be the ends 

 of the chromatin threads which project further. 



Moreover, I am unable to confirm the presence of " two 

 cleft-shaped cavities on the outer surface of the daughter 

 plates," which are said to be " separated from the plasma by 

 a thin and somewhat less transparent layer," and to be filled 

 with nuclear fluid. I would add that, by using a suitable 

 method of fixing, at this stage in the non-vacuolate plasma 

 lying between the plates I was able to observe a fine striation 

 running from one side to the other, and, further, that in some- 

 what more advanced stages the future plane of severance is to 

 be found already indicated halfway between the plates. 



I will here pass lightly over the further processes leading 

 to the reconstruction of the daughter nuclei. They consist 

 in the plates becoming bent, each with the concave side 

 towards the other plate, so that each of them assumes the 

 shape of a bowl. Then they gradually become more and 

 more rounded off, until finally even the last small depression 

 disappears. The further changes in the structure of the 

 daughter nuclei, which, as also the mother nucleus, exhibit a 

 tine membrane, represent a retrograde recapitulation of the 

 first pro-phase stages. The arrangement of the chromatin in 

 the shape of a thread, which still remains distinctly visible 

 for some time, especially in the outer layer of the nuclei, at 

 last gives way to the spongy disposition characteristic of the 

 resting condition of the nucleus of Aulacantha. 



After the daughter plates have already become transformed 

 into cup-shaped structures, we recognize on the exterior of 

 the central capsule the first indications of the constriction 

 which now commences. This is aimounced by the appear- 

 ance on the aboral side of a slight groove, which, running 

 vertically to the frontal plane, gradually advances further and 

 further, and tinally divides the central capsule into the two 

 daughter capsules. Thus, in opposition to what we find in 

 direct division, binary fission of the main aperture does not 

 set in until a relatively late period. 



I would remark, further, that no trace of a nuclear spindle 

 and centrosomes could be discovered. 



Besides the nuclear stages already alluded to we find others 

 that fit into none of the developmental series discussed above, 



