No. I.] SPERMATOGENESIS OF BATRACHOSEPS. IJ 



chromioles. A chromosome is built up of a certain constant 

 number of chromomeres without any other additional part than 

 a chromoplast. A chromosome may thus be termed a string 

 of chromomeres attached to a chromoplast. The formation of 

 chromosomes is of a necessity different in the different varie- 

 ties of cells. In the polymorphous spermatogonia, where a 

 resting stage occurs in the nucleus, the chromosomes originate 

 from leaders or strings of chromioles, in the way that has been 

 partly described in the preceding paragraph. This is the case 

 also in the auxocytes. The leaders finally contract, their 

 chromomeres approach each other and finally fuse. When 

 the required number of chromomeres have formed, the leader 

 splits lengthwise, and shortly afterwards the two halves sepa- 

 rate and spread out. At the same time the chromoplasts 

 divide in as many parts as there are leaders, one part remain- 

 ing attached to each leader (Fig. 122). The next step is a 

 further contraction of the leader, which again is followed by 

 a twisting of its free ends, thus forming the bretzel-shaped 

 chromosome. The mitosis of the chromosomes will be treated 

 under the heading of mitosis. 



In the spermatocytes the chromosomes appear from the 

 confluent umbrella stage in the form of staples, with strongly 

 marked chromomeres, and with the chromoplast attached to the 

 angle of the chromosome instead of to the end of one of its 

 arms, as in the auxocytes. The chromosome in each cell 

 variety is characterized by a certain number of chromomeres ; 

 in the auxocytes and spermatocytes they are six, though now 

 and then we find some chromosomes larger than others. When 

 such is the case we at the same time find very small chromo- 

 somes with a smaller number of chromomeres, thus making the 

 number of chromomeres and chromioles the same for every 

 nucleus of the same kind of cell. In the mitosis of the poly- 

 morphous cells we find the number of chromosomes to be 

 twenty-four, but in the auxocytes, as well as in the spermato- 

 cytes, the number of chromosomes is reduced to twelve. The 

 reduction in number takes place in resting stages of the auxo- 

 cyte, and is due to the chromoplasts which project only twelve 

 leaders instead of twenty-four, as in the polymorphous cells. 



