ROBERTSON: THE CHROMOSOME COMPLEX. 281 



SYEBULA ADMIRABILIS. 



of such as figure 20 a coiled spireme similar to what McClung 

 ('02) has described for the Locustidse. At first this spireme 

 is very irregular and difficult to outline (fig. 23), but later it 

 becomes as clear cut as any ordinary metaphase chromosome, 

 though much more coiled (figs. 24, 25). It gradually shortens 

 and thickens, as shown in 26, 27 and 28, and finally arrives 

 at the metaphase as a short, compact, almost straight rod 

 (figs. 30-36). The accessories of figure 25 are from nuclei 

 of the cyst which contains figure 24, those of figure 27 from 

 that containing figure 26, and those of figure 28 from the 

 cells of a cyst that is still farther advanced than any of these. 

 As well as showing the gradual shortening and thickening that 

 the accessory undergoes, these figures show the many shapes 

 that it may assume in various nuclei that are at the same 

 stage in development. From the time that it enters the spi- 

 reme condition it becomes perfectly smooth in contour, con- 

 trary to what we find in many Acndidse, where in the late 

 prophase or the metaphase it is often woolly. No indication 

 of a longitudinal split has been noticed in this spireme condi- 

 tion, although it might be expected to be present. And lastly, 

 there is no evidence of a transverse constriction such as Mont- 

 gomery claims for S. acuticornis. 



We have now traced the accessory from the resting period 

 of the spermatogonia through to the spermatoc3i;es. At times 

 there was difficulty in recognizing it, especially in the sperma- 

 togonial prophase, where it had a tendency to form a network 

 like the other chromosomes, but even there we were able to 

 tell it by its peculiar vesicle. After the last spermatogonial 

 division it was always recognizable by its condensed, homo- 

 geneous appearance and by its peculiar position, applied close 

 against the inner side of the nuclear membrane. During all 

 this time there has been no indication of its being a paired or 

 bivalent structure. We have seen no segmentation of the 

 spireme in the vesicle stage of the spermatogonia, no paired 

 condition in the spermatogonial metaphase where the chro- 

 mosome number was odd, not even, and no paired condition 

 in the growth period following the last spermatogonial divi- 

 sion, where the additional chromatin-like structure present 

 was found to be a nucleolus, not a chromosome. And lastly, 

 we have seen no transverse constriction or a bending at any 

 particular place that would in any way indicate the bivalency 



