The spermatogeue>.):> of Peripatus (Peripatopsis) balfouri. 351 



vesicular stage of the chromosomes is particularly characteristic of 

 the mitoses following upon the maturation divisions. 



Finally, a word as to continuous and discontinuous chromatin 

 spirems. In the prophases of spermatogonic and ovogonic mitoses it 

 seems to be the general rule that a continuous chromatin spirem 

 occurs, i. e. that the chromatin granules become evenly distributed 

 along the linin spirem. On the other hand, it has been definitely 

 shown for some cases, that in the prophases of the 1st maturation 

 divisions there appears to be no stage of a continuous chromatin 

 spirem, i. e, that the chromatin remains distributed at only certain 

 particular points on the linin spirem. Probably this is directly re- 

 ferable to the grouping of the univalent chromosomes into pairs 

 before the maturation divisions. Perhaps it will be found to be a 

 general rule that the ovogonic, spermatogonic and somatic mitoses 

 differ from the maturation mitoses in this regard. 



3. The Movements of the Chromatin. 



There are three possible views of the movement of the chro- 

 matin: 1) it is an automatic action of the chromatin, and then the 

 linin would be only the path of its movement ; Boveri first clearly 

 expressed this view; as expressed by Brauer (1893): "Die Lininfäden 

 sind .... auf diesen Stadien nur die Bahnen, in denen sich das Chro- 

 matin activ bewegt". Or 2) the chromatin is passive, and is moved 

 about by automatic movements of the linin ; a view held by a number 

 of observers. Or 3) the whole nuclear element, i. e. the linin spirem 

 with the chromatin arranged on or in it, may be looked upon as an 

 automatic whole, with power of movement in its different parts; this 

 possiblity has I believe not been considered. 



Now in Penfatoma and Peripatus, in the 1st maturation division, 

 the mantle fibres of the spindle are certainly derivatives of the linin 

 of the nucleus, of the distal linin fibres; and it is pretty generally 

 held that the mantle fibres are contractile structures. But whether 

 in general the linin spirem possesses contractility, 1 have found no 

 means of determining. Thus in the synapsis stage, are two univalent 

 chromosomes pulled together along the central linin thread by its 

 contraction, or do they move automatically along this thread? If the 

 linin spirem had the power of contraction and expansion equally in 

 all its parts, and in such a way that all parts must expand or con- 

 tract simultaneously, a union of univalent into bivalent chromosomes 

 could not be effected. If the linin spirem expanded and contracted 



