The spermatogenesis of Peripatus (Peripatopsis) balfouri. 353 



wlicrc the uucleus lies I have called the central pole of the cell; and 

 the opposite pole, characterized by the greatest amount of cytoplasm 

 and yolk, and containing the idiozome body (sphere), I have called 

 ihe distal pole ; the latter is further characterized by the Zwischeu- 

 körperchen plate which persists for a long period. 



It is interesting that an exactly similar relation of polarity and 

 nucleus seems to obtain in some other forms. Kingsbury (1899) 

 gives a figure of the synapsis of Desmognathus in which the chromatin 

 loops show exactly the same polarity as in Peripatus: "During this 

 period the chromatin thread (or threads) shortens and thickens, and 

 finally may be resolved into twelve horseshoe-shaped loops, which, in 

 most cases at least, are so arranged as to have their ends — the 

 open side of the loop — opposite the centrosphere." Eisen (1900) 

 shows in his fig. 3 a lateral view of a "bouquet stage" (synapsis) of 

 a spermatocyte of Batrachoscps, which shows the same polarity. Then 

 Lee (1897, figs. 8, 10) figures similar polar relations for Helix, as 

 does also Platner (1886). And v. Erlanger (1896) writes of the 

 nucleus of spermatocytes of Phyllodromia : "seine chromatischen Ele- 

 mente bilden Fäden, welche zu einem Büschel vereint von einem 

 Punkte der Kernmembran ausstrahlen. Dieser Kernpol ist dem Centrum 

 der Zelle zugewendet", and in this centre lies the Nebenkern. 



My observations on Peripatus show that the angles of the bi- 

 valent chromosomes in the synapsis mark the unions of every two 

 univalent chromosomes (Plate 25, diagrams 260, 261) ; and that these 

 angles are directed towards that pole of the cell furthest from the 

 idiozome mass. Accordingly, whenever the reduction of the number 

 of chromosomes is effected by a union of the univalent chromosomes 

 into pairs in the anaphase of the last spermatogonic mitosis, I would 

 consider that in all objects, just as in Peripatus^ these pairs become 

 so disposed that their angles point to one pole in the nucleus (that 

 pole nearest the original pole of the preceding achromatic spindle), 

 and that their opposite ends point towards the opposite pole of the 

 nucleus. As a corollary of this conclusion, it would follow that in 

 other objects as in Perij^atus, the angles of the bivalent chromosomes 

 in this stage mark the points of union of univalent chromosomes. Thus 

 the polarity of the chromosomes in the first spermatocytes would be 

 a representation of the reduction in number of the chromosomes. 



In expressing this conclusion I am fully aware of the dangers in 

 attempting to draw homologies between Peripatus and forms which I 

 have not examined; but the descriptions of Eisen, Kingsbury, 



ZooL Jahrb. Ï1V. Abtb. f. Morph. 23 



