ROBERTSON: THE CHROMOSOME COMPLEX. 303 



SYKBULA ADMIRABILIS. 



trary, it was found to be, under all conditions and at all times, 

 a univalent chromosome. 



3. In the prophases of the spermatogonia two deeply stain- 

 ing nucleoli are usually present. In the telophase of the last 

 division and in the early part of the growth period following 

 they are still present, staining red with safranin, like the ac- 

 cessory. In the middle and later growth period there is but 

 one large nucleolus present, almost as large as the accessory. 

 It fades out and disappears as the chromosomes enter the late 

 prophase of the first spermatocyte and begin to condense. 



4. There are twelve chromosomes in the first spermatocyte. 

 No exceptions to this were found in a series of fifty or more 

 cells that were examined, belonging to at least a dozen different 

 animals. The chromosomes consist of rings, semiclosed rings, 

 crosses, bent rods and straight rods. All of these forms may 

 be considered as modifications of a single type, that of a rod 

 with one longitudinal and one cross division. The cross divi- 

 sion locates the point at which the spermatogonia! pair conju- 

 gated by their proximal ends. This rod has the ability to 

 change its long axis from a longitudinal to a transverse direc- 

 tion. All chromosomes of the first spermatocyte, except the 

 accessory, pass through this process of change of axis. The 

 cross form represents merely a transition stage in the process. 

 Rings are merely spermatogonia! pairs that have conjugated 

 at both proximal and distal ends. Semiclosed rings, kidney 

 shapes, bent rods and straight rods are those that have con- 

 jugated by the proximal end only. All the ordinary chromo- 

 somes divide in the first division. They divide longitudinally 

 (equationally) not reductionally. The accessory does not di- 

 vide but passes over complete to one of the resulting daughter- 

 cells. 



5. One half of the second spermatocytes therefore contains 

 eleven chromosomes and the other half eleven plus the acces- 

 sory. These dyads here correspond to pairs of homologous 

 spermatogonia! chromosomes. They are divided crosswise or 

 reductionally. It is here that the maternal and paternal ele- 

 ments are separated from each other. The accessory divides 

 longitudinally here like it did in the spermatogonia. One half 

 the spermatids receive eleven chromatids and the other half 

 twelve. This of course insures a dimorphism of the protozoa. 



6. The chromosomes show individuality of size and, to a 



