STUDIES ON CHROMOSOMES 371 



cases, as already mentioned, was described by Janssens in Triton. 

 The chromatin-masses ('blocs') from which the spireme-threads 

 unravel are here of irregular shape, and show no polarization, but 

 are nevertheless believed to be directly traceable to the preceding 

 telophase-chromosomes. The threads are already in evidence in 

 the latter, and sometimes show an irregularly spiral course 

 (Janssens's fig. 80) but in the later stages are irregularly convo- 

 luted in a manner very similar, as far as can be judged from the 

 figures, to that seen in the pre-synaptic stages of the grasshoppers. 

 Janssens emphasizes his belief that in general a single thread is 

 formed from each 'block,' though in certain cases the latter are 

 double and give rise to two threads. An essentially similar proc- 

 ess is described for the pre-synaptic stages. "La premiere trans- 

 formation qa'on observe dans les auxocytes est analogue a celle 

 qui annonce le commencement de la division dans les spermato- 

 gonies . . . . et consiste en un resolution des blocs de 

 nucleine" ('01, p. 68). An essentially similar phenomenon in 

 the spermatogonial prophases is brilliantly demonstrated in two 

 a4mirable slides of Phyrnotettix by McClung, one stained with 

 iron haematoxylin, the other by Flemming's triple method. In 

 this form the 'chromatin blocks' are elongate and polarized (fig. 

 93, photos. 29 to 31), and the thread later forms a beautiful and 

 very definite spiral, as was first described by Pinney (08). This 

 observer describes the spiral threads as formed separately within 

 the vesicles or sacculations to which the preceding anaphase- 

 chromosomes give rise (as first made known by Sutton '00, in 

 Brachystola and confirmed by several others subsequently). 



As far as can be judged from the figures and brief description of 

 Pinney, the threads are formed as rather loose and open spirals 

 directly out of a fine reticulum within each chromosome-vesicle. 

 The rather limited material at my disposition shows somewhat 

 different conditions, though confirming the main point. The con- 

 ditions in McClung's slides differ from those described by Pinney 

 in that none of the resting nuclei or early prophases show the 

 nuclear sacculations so distinctly, nor is the chromatin so diffuse — 

 differences which may well be due to the fact that none of the 

 earlier generations of spermatogonia are shown. In these nuclei 



