62 SYDNEY J. HICKSON. 



nuclei are about to divide again reappears in the form of 

 extremely minute granules, which fuse together to form the 

 chromosomes of the next division. 



A similar disappearance has been described in the unfer- 

 tilised egg of Rhodites, and in this form there is no mem- 

 brane surrounding the nuclei. 



These researches prove, then, that in some insects there is 

 a " disappearance" of the chromatin substance of the nucleus 

 after its first division. 



To what is this disappearance due ? Henking thinks that 

 it is due to some chemical change in the chromatin substance, 

 as in some cases the outline of the chromosomes may be ob- 

 served after the disappearance of the colouring matter. Never- 

 theless it is a fact that commonly the chromosomes lose their 

 compact form during the colourless stage, and become very 

 finely divided. We can attribute the disappearance, then, 

 partly to the change in the chemical character of the chro- 

 matin, and partly to the very minute and scattered condition 

 of its elements. 



Further, in some cases (Rhodites) not only does the chro- 

 matin disappear, but also the membrane surrounding the 

 nuclear area, so that we have (as in Distichopora, &c.) a 

 condition in which the nucleus is practically indistinguishable 

 from the surrounding protoplasm. 



It is during this condition that some of the nuclear fragments 

 may be distributed through the substance of the ovum, and 

 give use to the nuclei of the so-called "free nuclear formation" 

 by subsequent fusion. 



It must be obvious to anyone who carefully studies 

 Henking's figures that in many insects the spindle of the first 

 division of the oosperm nucleus is very irregular, that the 

 chromosomes are not always arranged with the same mathe- 

 matical precision that they are in typical karyokinetic figures, 

 and further, that in consequence of the disappearance and 

 extremely fine division of the chromatin substances there are 

 still some steps in the nuclear divisions at the commencement 

 of development which have not been satisfactorily traced. 



