e 9, PAL Sek. ws 
I 
DAVIS: SPERMATOGENESIS. 12% 
pole, as described by the Schreiners, but believe this an accidental 
arrangement, which is more common near the pole, since in this 
region the threads are crowded more closely together. Moreover it 
seems hardly probable that the chromosomes should conjugate granule 
by granule. 
Among the species in which the Schreiners have described the side 
by side union of the chromosomes is Salamandra, but both Montgom- 
ery (:03, :04) and Moore and Embleton (:06) have found an end to 
end union in closely related urodeles. 
According to the Schreiners each of the polar loops later becomes 
converted into a tetrad in the following way: ‘The two conjugants 
become widely separated, remaining connected only at one or both 
ends, to form loop- or ring-shaped elements, and at the same time a 
longitudinal split appears in each conjugant. ‘This necessitates a 
very rapid shortening and thickening of the chromatic threads and the 
simultaneous appearance of a longitudinal split, but on both these 
points their figures are far from convincing. 
It will be seen that the end result is the same as in Orthoptera, 2. e. 
that the longitudinally split arms of the loops, or the opposite sides of 
the rings, represent the univalent components. 
The types of bivalent chromosomes described by these authors 
in the prophase of the first division strikingly resemble those found in 
the Orthoptera. 
4. THe MArTuRATION DIVISIONS. 
The extensive literature on this important stage in the development 
of the germ cells has been so often, and so thoroughly reviewed that 
it will be unnecessary for me to attempt an extended discussion here. 
The entire problem of maturation is at present in a very unsatisfactory 
state and there seems to be no prospect, for some time at least, of 
reducing the widely diverse accounts to a common basis, although 
the striking similarities in the shape and behavior of the bivalent ele- 
ments in widely separated forms leads to the hope that in time this 
may be accomplished. 
In any discussion of the subject the method of formation of the 
bivalent chromosomes must be taken into account and this has, of 
course, been done only within very recent years. For this reason the 
older accounts of the maturation division — such as those of Boveri 
(87), Flemming (’88), Hertwig (90), Brauer (93), Meves (’96), von 
Lenhossék (98), McGregor (’99), and Kingsbury (:02), in which 
