The spermatogenesis of Peripatus (Peripatopsi^) balfouri. 323 



be readily referred to that of the synapsis and telophase; only then 

 is the lon.^itiidinal split of each univalent chromosome clearly marked; 

 and only then, as a rule, is the central liniu fibre {C.P.L Figs. 135, 

 13G, 139 — 160, Plate 21) clearly distinguishable since it later becomes 

 more or less covered up by the chromatin, only to reappear in the 

 nietakinesis and then in the form of a connective fibre. We shall 

 tind that the 1st maturation metakinesis separates entire univalent 

 chromosomes, i. e. is a transverse division of the bivalent chromosome, 

 exactly as in Insects; accordingly the constriction marked by the 

 central linin thread may be called here, as in Insects, the transverse 

 si)lit of the chromosomes. As the figures show, this transverse split 

 may lie perpendicular to the long axis of the bivalent chromosome, 

 and this is the case with all those of an elongate dumbbell shape: 

 but in those where the two univalent chromosomes lie parallel and 

 close to one another, the whole bivalent one may be likened to a 

 very much flattened dumbbell (a dumbbell with the ends pushed 

 together), so that in these cases the transverse split, instead of being 

 perpendicular, is parallel to the long axis of the chromosome (compare 

 the chromosomes in Figs. 161 — 181). 



But in definitive chromosomes of a ring shape, and in others 

 which depart widely from the usual type of a bent dumbbell, what 

 means can be found for determining the position of the central and 

 distal ends of the chromosomes? Without some sure method of deter- 

 mining this question, we cannot explain how such chromosomes become 

 divided in metakinesis. Now in the early prophases the axis of each 

 univalent chromosome is formed by a matrix of linin, the axial linin 

 fibre; at the central end of each univalent chromosome is a com- 

 paratively thick baud of linin, the central band, which connects this 

 chromosome closely with the central end of another univalent chromo- 

 some; and then attached to the distal end of each chromosome is a 

 comparatively thick linin fibre, the distal linin fibre. All these linin 

 structures, with the exception of the axial linin band which is covered 

 and so hidden by the chromatin , can be clearly seen whenever they 

 lie in the plane of the section (compare Figs. 135, 136, 138, 141 — 149, 

 153 — 161, 163—170). The relations of these threads to the chromatin 

 is the same as in the preceding synapsis and telophase (compare the 

 figures on Plate 20), and on this account not only may the same 

 terms be applied to them, but also they may be regarded as morpho- 

 logically identical with such fibres of linin. And as in those earlier 

 stages it seemed very probable that central, axial and distal threads 



21* 



