CASTLE: EMBRYOLOGY OF CIONA INTESTINALIS. 217 
by the different tints of blue which they exhibited. Iron heematoxylin 
was sometimes employed instead of Ehrlich's, but the results were no 
better — indeed not so good — for the differentiation of organs or their 
fundaments. 
For studying the processes of maturation and fertilization sections 
alone could be employed on account of the opacity of the eggs. In mak- 
ing seetions of these stages orientation was of course impossible, so that 
a large number of the eggs was embedded together, without previous 
decortication, and cut at random. The egg membranes, so far from 
being an obstacle, were at these stages a positive advantage, since they 
served to protect and hold the polar globules in place. The material 
employed in the study of maturation and fertilization stages was killed 
either in Perenyi's or in Hermann’s fluid, the best results being obtained 
from the former. For convenience the killing of each day will be referred 
to as a series (A, B, or C), made up of lots (1, 2, 3, etc.) which were 
killed at intervals of about ten minutes, the first lot being killed as soon 
after the laying as a sufficient number of eggs could be collected, usually 
about five or ten minutes. 
IV MATURATION AND FERTILIZATION. 
The eggs of series A, lot 1, show an early stage in the process of matu- 
ration, namely, the formation of the first polar globule. Figure 1 repre- 
sents a section through one of the eges of this lot most advanced in 
development. The egg envelopes, which rest close down upon the egg, 
are left out in this and all the other figures. Already at this stage we 
reeognize that the egg is made up of two unlike hemispheres, one richer 
in yolk, the other richer in protoplasm. The former occupies the future 
dorsal or endodermal side of the egg, and at the centre of its surface, as 
stated in my preliminary communication (94), the polar globules form. 
The cell division which will give rise to the first polar globule is seen in 
this figure to bo already well advanced, the chromatin being accumulated 
at the two ends of the spindle. About the deeper end of the spindle there 
is a small space free from yolk granules and oceupied by a finely granular 
deeply staining mass of protoplasm, of which we shall have more to say. 
The entire remainder of the dorsal hemisphere, except that small portion 
of it occupied by the spindle itself, is filled with rounded yolk granules 
(cf. Fig. 2) of a rather uniform size, closely packed together, but with 
slender films of staining protoplasm passimg between and around them. 
Davidoff's (789) beautiful figures, particularly his Tafel VI. Fig. 33, 
D 
VOL. XXVII. — NO. 7. 
