1896. | NEW YORK ACADEMY OF SCIENCES. 165 
insolvable in this form; for previous to the formation of the 
asters the centrosomes could not be distinguished from the nu- 
merous nuclear as well as cytoplasmic granules. This black 
centrosome granule seems to be the only structure at the focus 
of the rays, and shows no trace of a surrounding archoplasmic 
mass, apart from the radiating fibrille of the aster. As yet no 
chromosomes have been definitely established, though here and 
there are to be observed slight thickenings or bunching together 
of strands of the chromatic reticulum which is doubtless the 
prelude to chromosome formation. There is also present in 
this stage a large dark staining nucleolus, situated eccentricly 
within the nucleus. The nucleus lies very nearly in the center 
of the egg, and the deutoplasm is pretty evenly distributed in 
the surrounding cytoplasm. (Fig. 1.) 
From now on the size of the asters and the number, length 
and distinctness of the rays steadily increases.* The nuclear 
membrane meanwhile becomes more and more pushed into the 
folds by the ingrowing spindle fibers in essentially the same 
manner as described by Watasé (Squid), Wheeler (Myzotomum), 
Braus (Salamander) and others. The deepening of the folds 
continues until at length the nuclear membrane commences to 
break apart at the apices of the folds. Through the openings 
thus formed the rays enter the nucleus, while the intervening 
portions of the membrane seem to be drawn into the polar sys- 
tem and pass insensibly into rays. (Fig. 2.) Typical tetrad 
groups, to the number of nine I believe, are meanwhile -esta- 
blished, and before the membrane has commenced to fade a 
small centrosphere is differentiated about each centrosome. In 
some cases, at least, the latter becomes double even at this 
early period, by an extremely precocious division in anticipation 
of the second polar division. 
In most cases the asters develop independently, unconnected 
with each other by any sort of central spindle. The definitive 
spindle finally arises by the meeting of rays from the opposite 
asters. In two or three cases, however, where for some reason 
the asters had not diverged far, but remained comparatively 
near together, I observed what seemed to be a central spindle 
connecting them, in a stage corresponding to Fig. 2. It is 
figured in Fig. 3. The difference is probably due to variation 
in the relation between divergence and growth of the asters. If 
great divergence takes place while the asters are yet small, as 
usually the case, no such “ central spindle” is formed, but the 
appearance shown in Fig. 2 results. If, on the other hand, the 
_* This progressive elongation of the rays with the growth of the aster agrees with 
Driiner’s account of the spermatocytes of the Salamander. 
