The spermatogenesis of Peripatus (Peripatopsis) balfouri. 319 



preserved their integrity from the time of the last spermatogoiiic 

 division, are gradually being more separated from one another by a 

 l)rocess of contraction on the part of each chromosome. 



All the chromosomes now show, with more or less distinctness, 

 the form characteristic of the synapsis and telophase namely the 

 shape of two longitudinally split rods making together a V or U, the 

 angle or bend of which is formed by a band of linin (Figs. 1.85—161, 

 Plate 21). They have not, however, the orderly arrangement found 

 in the early telophase, where the central poles of the chromosomes 

 were directed towards one part of the nucleus, the distal ends towards 

 an opposite pole, but are much more irregularly disposed; this ir- 

 regularity is probably directly referable to the changes the chromo- 

 somes had undergone in the rest stage. But the fact that the chromo- 

 somes are in exactly the same number, and show very much the same 

 form, now as they did before the rest stage, is a strong corroboration, 

 it seems to me, of the conclusion that they had preserved their inte- 

 grity through that rest stage. 



Each chromosome now, as before the rest stage, is seen to be bi- 

 valent, composed of two univalent chromosomes whose central ends 

 are joined by a band of linin (central linin band); further, in the 

 early prophase, each univalent chromosome is seen to be longitudinally 

 split (Figs. 135, 136, 139—147, 149-155, 157-160). The main 

 differences from the chromosomes of the synapsis and telophase are: 

 the chromosomes of the maturation mitosis are more irregular in 

 form; in them the longitudinal split is less distinct; and in each uni- 

 valent component the chromatin granules form a continuous line of 

 chromatin. 



These chromosomes differ from one another in form more in the 

 early prophases than they do when they attain their definitive form; 

 the latter form is reached by a process of gradual shortening up of 

 the chromosomes and condensation of the chromatin granules, whereby 

 the longitudinal split becomes hidden. A glance at the figures shows 

 how multifarious the shapes of the chromosomes are in these stages 

 (Figs. 135-165, Plate 21; Figs. 166-182, Plate 22); but they may 

 all be referred to 4 main types, the evolution of each of which may 

 be examined in succession. 



1) Bivalent chromosomes in which the central ends of the two 

 univalent chromosomes are connected rather closely by a band of linin 

 (central linin band), while the distal ends of the chromosomes are 

 not connected together (Figs. 135, 136, 138-141, 144, 147, 148, 



