THE DEVELOPMENT OF THE CAPE CEPHALODISCUS. 207 
advanced larvae the nervous tissue is seen to extend in a 
posterior direction under the general tissue of the ectoderm 
(PI. 14, fig. 32), and the cells of the sense organ now assume 
the same character as this nervous tissue. They lose their 
cilia, and become sunk in an ectodermal pit (PL 14, fig. 33), 
which may be drawn out posteriorly into a tubular structure 
(PL 14, fig. 35, inv.s. o.). 
(5) A postero- ven tral thickening and involution 
of the ectoderm was observed in some sections under the 
hinder end of the yolk mass. This thickening is seen in 
Pl. 14, fig. 23, and, a few -sections posterior to it, it is seen to 
lead to an involution. This involution is, however, more clearly 
seen in another series (PL 14, fig. 36). It may not prove to 
be of any particular significance, but may be noted, as it is in 
this region that the greatest change will probably take place 
in the metamorphosis of the larva. 
Summary of Results. 
(1) Certain facts are noted with regard to the formation of 
yolk granules, presence of yolk nuclei, character of nucleus 
and nucleolus. 
(2) The segmentation is holoblastic, equal, or markedly 
unequal, and apparently indeterminate. 
(3) A blastula stage occurs. 
(4) The blastula becomes solid by proliferation of cells at 
one end ; there is no invagination at this stage. 
(5) The point of proliferation marks the posterior end, 
and the anterior end is distinguished by the elongation of its 
cells. 
(6) All the outer cells become elongate, and assume the 
character of columnar cells full of yolk. As these increase in 
number a small posterior invagination appears. 
(7) The cellular character of the yolk columns disappears; 
the yolk granules are used up, and an ectoderm consisting of 
many nuclei in a protoplasmic network, with a basement 
membrane, is formed. 
