CASTLE: EMBRYOLOGY OF CIONA INTESTINALIS. 219 
nent than those running in other directions. Along them as radii 
doubtless protoplasm is passing to augment the yolk-free area. Nothing 
in the nature of “fibres” has been observed in them.  Excentrically 
situated in the yolk-free area (Fig. 4) is seen the male pronucleus, a 
perfectly clear oval body, with a delicate but sharp boundary. Its long 
axis lies radially with reference to the attraction sphere, which mani- 
festly exerts on it a directive influence. igure 4 represents the eleventh 
of a series of eighteen sections. The sixteenth section of the series is 
shown in Figure 3. It contains the second maturation spindle, at either 
end of which is an attraction sphere in the centre of a slight accumula- 
tion of protoplasm. The chromosomes cannot be clearly made out, but 
perhaps lie aggregated in a small dark mass close down against the 
attraction spheres. It is evident that the amount of chromatin in- 
volved in this division is less than in the case of the first maturation 
division (cf. Fig. 1). The obliquity of the plane of sectioning to the 
dorso-ventral axis of the egg makes this spindle appear to lie quite a 
little below the surface of the egg. Such, however, is not the case; it 
comes close up to the surface, but, obliquely, not vertically, as did the 
first maturation spindle. Indeed, am examination of othor specimens, 
less advanced, shows that it first appears in a horizontal position, i. e. 
ab right angles to the direction of the first maturation spindle as seen in 
Figure 1, but later rotates so that one end of the spindle lies deeper in 
the egg than the other. The first polar globule does not really lie in 
this section, but has been projected there from its real position on the 
margin of the next section, the seventeenth of tho series. 
In Figure 5 is represented a section, the fifth of a series of sixteen, 
through an egg of Series A, lot 3, killed twenty minutes later than 
lot 1 of tho same series (cf. Fig. 1). The section passes obliquely in a 
dorso-ventral direction, unlike those shown in Figures 2—4, which were 
more nearly horizontal. On the ventral margin of the section is seen the 
eap of protoplasm which as early at least as the beginning of maturation 
covered that side of the egg. The male arehoplasm has moved deeper 
into the egg, and its attraetivo influence has been extended so that 16 is 
now manifested over the greater portion of the section. In consequence 
of this attraction on the protoplasm the area free from yolk has con- 
1 A rotation of the maturation spindles from an original tangential to a radial 
position has been observed repeatedly in other animals; in the ease of the second 
spindle, the tangential position is doubtless correlated with the derivation of its two 
archoplasmic masses from the single archoplasmic mass left in the egg after the 
completion of the first maturation division. 
