2O2 MAULSBY W. BLACKMAN. 



one or several large nucleoli of pure chromatin from which are 

 derived the chromosomes of the succeeding division. In the 

 maturation of the egg of Distaplia, Davidhoff, '89, has observed 

 similar phenomena. 



C. Schleider, '91, believes that the large nuclei found in the 

 eees of Echmodermata are but reserve masses of chromatin. 



o o 



That this is true under some conditions at least, is shown by the 

 recent experiments of R. Hertwig, '96, and Wilson, 'or. Wil- 

 son finds that, in one series of eggs chemically fertilized with 

 MgCl solution, the chromosomes functioning in mitosis are ob- 

 tained by the breaking down of the large densely staining 

 " nucleolus." " Its contour becomes irregular and its texture 

 loose. A little later it assumes a spongy appearance and short 

 irregular processes are extended from its periphery. Enlarging 

 still more it now gives almost the appearance of a close, broken 

 spireme from the ends of which chromatin threads here and 

 there project." These threads later form the chromosomes. As 

 will be readily seen this process in Toxopncustes is very similar 

 in many respects to that occuring in Scolopendra. 



The chromatin segments as they arise from the karyosphere 

 in Scolopendra are long, slender, granular filaments usually con- 

 siderably curved and distorted (Figs. 10, 1 1, 12). They are 

 arranged irregularly throughout the nuclear area supported by 

 the limn reticulutn. Very soon after their detachment from the 

 karyosphere, they are seen to be divided longitudinally along 

 their entire length. Owing to the length and distortion of these 

 segments they frequently assume very fantastic shapes. In some 

 cases the two parts are coiled or twisted about each other like the 

 strands of a rope (Fig. 11) while the two halves of other chro- 

 mosomes may be separated by a considerable distance (Fig. 10). 

 This cleavage of the segment very evidently represents the lon- 

 gitudinal division of the chromosome, and as the chromosome is 

 first divided in this manner in the prophase it is, I believe, justifi- 

 able to conclude with McClung, 'oo, that the first maturation 

 mitosis accomplishes the equational division of the chromatic ele- 

 ments. Apparently the next change in the structure of the split 

 segments is shown in Fig. 13, a. This first becomes apparent as 

 a weakening of the two parts of the segment at about their mid- 



