The spermatogenesis of Peripatus (Peripatopsis) balfouri. 321 



another so as to form the figure of an X, are found all modifications 

 (Figs. 135, 137, 139, 141, 142—145, 147, 149, 152, 154, 163, 173, 

 174). In the typical X-shaped chromosomes the two univalent chromo- 

 somes approximate only at their middle points, though their central 

 ends still remain connected by the central band of linin (Figs. 141, 

 144, 154). Thus the chief peculiarity of the chromosomes of this sub- 

 type is in the comparatively wide separateness of the central ends of 

 tlie univalent chromosomes, i. e. in the length of the central linin 

 thread. At first I inclined to the view that for such X-shaped 

 chromosomes two of the openings of the X represented an unusually 

 wide, divergent longitudinal split, so that the two univalent chromo- 

 somes together would present the form of two V's joined at their 

 apices; were this the case, these chromosomes would differ from all 

 the others in possessing an unusually broad persisting longitudinal 

 split. But this view is erroneous. An X-shaped chromosome is formed 

 of two univalent chromosomes, each of a more or less straight rod- 

 form, which lie across one another at their middle points, and whose 

 widely separated central ends are still connected by the central linin 

 baud; at an early stage the longitudinal split is clearly seen in the 

 longitudinal axis of each univalent chromosome, so that none of the 

 openings of the X have any relation to this split (Figs. 145, 147, 

 149, 153, 154). In these chromosomes the longitudinal split, as in 

 all the other chromosomes, disappears almost or entirely before the 

 definitive form is reached, which for the X-shaped chromosomes seems 

 to be usually that of a dumbbell indented at either end. In diagram 

 254, I— III, are represented the principal modes of evolution of the 

 X-shaped chromosomes, and all the stages here represented have been 

 seen in my preparations. 



3) Ring-shaped bivalent chromosomes, each composed of two bent 

 univalent chromosomes, so disposed together that the central end of 

 the one is in close contact with the corresponding end of the other, 

 and joined to it by the central linin thread, while their distal ends 

 are also in close contact but apparently without linin connection 

 (Figs. 141, 142, 146, 148, 150—152, 156, 160, 164). Each univalent 

 chromosome therefore forms approximately one-half of the ring; and 

 at an early stage, though it disappears later, a clear longitudinal 

 split can be seen in the long axis of each univalent chromosome, so 

 that the central space of the ring separates distinct univalent chromo- 

 somes and has no relation to the longitudinal sjilit. !Such a ring 

 assumes the definitive form by shortening and thickening into a ring 



Zool. Jahrb. XIV. Abth. f. Morph. 21 



