290 
W. E. AGAR 
in Avliich the spindle is fully developed, but the chromosomes 
are not yet arranged on the equatorial plate, is given in 
fig. 15 B. A metapliase, or earlj'- anaphase, of the first meiotic 
division is shown in fiof. 13. In d we see a tetrad ring-, 
breaking simultaneously through both points of attachment 
of the conjugants. In c we see the more usual condition, 
where one point of attachment has given way before the 
otlier, and the ring has straightened itself out. In a and « 
the dissociation has gone further, the constituents of the 
tetrad remaining attached by a thin thi’ead only. 
The complete series of chromosomes from a nucleus at the 
same stag’e is given in fig. 15 c. 
Fig. 14 shows two daughter-plates resulting from a first 
meiotic division. It is somewhat unusual for daughter-plates 
to be formed in this way in the meiosis of Lepidosiren, the 
chromosomes as a rule remaining bunched together near the 
two poles, while the spindles rotate for the second division. 
'I’he longitudinal splitting preparatory for the second division 
is, therefore, exceptionally well shown in this figure. Each 
chromosome again forms a tetrad, owing to the transversely 
constricted chromosomes of anaphase I having each divided 
lengthwise. 
The chromosomes forming the right-hand plate (some of 
which are in the next section) are shown in fig. 15 d. Only 
eighteen tetrads were present, one having evidentl}’^ been 
carried away by the razor. 
A consideration of the spermatogonial and meiotic figures at 
once shows a. very important fact, namely that the transverse 
segmentation of a given cliromosome always takes 
place at the same spot. In the case of the longer chromo- 
somes the segmentation is marked by the bend of the V, in 
the shorter ones by a transverse constriction. This constancy 
as to the point of bending or constriction can also be gathered 
from the somatic mitoses, but partly owing to the greater 
complexity of the figures it is not possible to demonstrate it 
so clearly as can be done in the gonadic divisions. 
In the four series of chromosomes shown in fig. 15 I have 
