Helen Dean King 359 
these various forms the chromosomes assume in the prophases of the 
first maturation mitosis, as frequently in the same nucleus some of the 
chromosomes have the form of dumbbells while others are in the shape 
of rings (Fig. 38). Nuclei containing chromosomes of different shapes 
are perhaps the most valuable for a study of this period in the develop- 
ment of the spermatocytes, as they show very clearly how the different 
types are related to each other and to the original spireme. Fig. 38 
shows a section of a spermatocyte in which the chromosomes are of 
mixed types. Three dumbbell-shaped chromosomes, in which the direc- 
tion of the first maturation mitosis is indicated by the constriction in the 
middle of the chromosomes, are connected with a ring-shaped chromo- 
some which shows only the second division. As these chromosomes are 
still united end to end by linin fibres there can be no question of the 
relation of these two types of chromosomes to each other and to the origi- 
nal spireme. | 
A section of another spermatocyte of the same character is shown in 
Fig. 39. In this case not only are the chromosomes of different types 
but they are also in slightly different stages of development. As the 
chromosomes are entirely separated it is not possible to determine their 
relation to the original spireme. This cell is unique in that it shows 
in the same nucleus chromosomes in which the first or the transverse 
division has already begun (dumbbells), chromosomes in which the 
second or the longitudinal division only is apparent (rings), and one 
chromosome which has already divided for both of the maturation 
mitoses (tetrad). 
Although ring-shaped chromosomes are found abundantly in the pro- 
phases of the first maturation mitosis, I have never found one of them in 
the equatorial plate of the spindle where they are always to be found in 
Salamandra, Amphiuma, and others of the Urodela. In a study of the 
spermatogenesis of Pedicellina americana, Dublin (11) found that the 
chromosomes have the form of rings in the prophase of the first matura- 
tion mitosis. When the spindle is formed these chromosomes elongate 
considerably, but still retain their ring-shaped character during the 
early metaphase. In the late metaphase the chromosomes lose their 
former shape and condense into elongated rods which divide transversely, 
the division being reductional. Thus Pedicellina seems to bridge over 
the gap between such forms as Salamandra and Amphiuma in which the 
ring-shaped chromosomes persist throughout the entire metaphase of 
the first maturation mitosis, the ensuing division being of the hetero- 
