A cytological study of the egg of Cumingia with special reterence etc. 245 
spermatogenesis of 2Iyxine, and that the spireme in the late prophase 
of somatic mitoses (Salamander) is also split so as to give the ap- 
pearance of a parallel arrangement of threads. Goldschmidt (’08) 
also has expressed his scepticism regarding parasynapsis and points 
ont the fact that similar appearances are seen in the germ-cells of 
parthenogenetic forms where there is no reduction. Since the nnmber 
of these paired rods is approximately eqnal to the reduced number 
of chromosomes, synapsis may here perhaps be interpreted as a trans- 
verse Segmentation of a longitudinally split spireme into half the 
somatic number, or as telosynapsis. But whatever the mode of 
synapsis, due to the subsequent history of the chromatic bodies 
(chromosomes?), it would still be impossible to make any definite 
Statement respecting the Order and significance of the maturation 
divisions in Cumingia. All that can be said is that the material from 
which the chromosomes will be formed has now appeared scattered 
through the germinal vesicle in the shape of chromatic masses fre- 
qnently seen in pairs. Daring subsequent early stages these bodies 
become aggregated into a larger mass (Figs. 4, 5 and 6) having the 
appearance of a closely-wound spireme. Sometimes this mass appears 
granulär presenting an arrangement of the prematuration chromosomes 
somewhat as described by Conklix ('02) for Crepidula and for Aste- 
rias forbesii by myself (’08), a condition which probably iudicates 
the beginning of the Separation of the definitive chromosomes (or a 
failure of dose union) in preparation for the transit to the spindle. 
Between the stages represented by Figs. 3 and 5 the cytoplasm 
passes from a pale reticular appearance through a stage in which 
it shows great affinity for basic dyes and has a granulo-alveolar 
structure to one in which it is again pale and alveolar but contains 
yolk-spherules which persist more or less abundantly to the time 
of the formation of the first polar spindle. 
At the culmination of the growth period the egg has enlarged 
about 1,500 volumes. Typically the large spherical deeply-staining 
nucleolus is situated dose to the nuclear membrane and at a point 
near the periphery of the egg. Between the nucleolus and the nuclear 
wall the chromosome-mass takes a position frequently in contact with 
the nucleolus. The first maturation mitosis is initiated by the appea- 
rance of an aster in the cytoplasm dose to that point of the nuclear 
wall next to the chromosome-mass. The single centrosome of the 
aster divides to form the amphiaster the two poles of which diverge 
almost to opposite poles of the nucleus. Meanwhile the nuclear wall 
16 * 
