THE RELATION BETWEEN AMITOSIS AND MITOSIS. 211 



the two forms of division varies in different chains, proglottids 

 and regions. Observations and experiments to be described later 

 will show very clearly, however, that amitosis as well as mitosis 

 is an important factor in growth, not only in Moniezia but in 

 many other forms and that in some cases at least either form of 

 division may be changed into the other by altering the conditions. 



These facts are of considerable importance as bearing upon 

 certain hypotheses regarding the significance of the chromosomes. 

 At present it seems improbable that the views held by certain 

 authors regarding the individuality of the chromosomes can be 

 reconciled with them. Extended discussion is, however, post- 

 poned until other facts have been presented. 



The most important features in the development of the male 

 germ cells in Moniezia are as follows : 



The testes apparently arise from cells which are already differ- 

 entiated as muscle-cells, as well as from other cells of the 

 parenchyma. The earlier divisions are almost entirely amitotic, 

 mitosis being rarely seen. 



The growth of the testis up to the time when spermatogenesis 

 proper begins is almost wholly by amitotic division. In the full- 

 grown testis the remaining spermatogonia still continue to divide 

 amitotically. After the spireme stage the spermatocytes follow 

 two very different lines of development. In some of them typi- 

 cal dyads are formed and the two usual spermatogenetic mitoses 

 follow : the spermatid nuclei are usually situated about the peri- 

 phery of large masses of cytoplasm, cytophores formed by fusion 

 of the spermatocytic cytoplasm, but may be isolated. 



In the other spermatocytes the nucleus increases in size, the 

 spireme breaks up into granules and masses and loses most of its 

 staining power, the old nuclear membrane disappears, and new 

 nuclear membranes form about small fragments of the chromatin : 

 each spermatocyte may give rise to several small nuclei : in ap- 

 pearence these nuclei are indistinguishable from the spermatid 

 nuclei produced mitotically. When first formed they are massed 

 in groups in the interior of the cytophore about spaces which 

 indicate the former positions of the spermatocyte nuclei. The 

 nucleolus does not take part in this fragmentation but remains in 

 the cytoplasm of the cytophore for some time. The nuclei thus 



