FORMATION OF GERM-LAYERS IN CRANGON VULGARIS. 9851 
sections represented in figs. 23 and 24; but it is in flat contra- 
diction to Kingsley’s statements, and to his remarkable fig. 
32 (second paper, pl. i), in which a black dot placed between 
the optic lobes is called the mouth. 
It is to be observed that during the stages of figs. 6 and 7, 
the ventral bands which form the blastodermic area occupy 
nearly half the surface of the egg. During the following 
stages a remarkable shrinking occurs; so that the Nauplius 
occupies a portion of the surface of the egg smaller than that 
occupied by the newly-established germinal bands. Kingsley 
has called attention to this shrinking of the embryonic area in 
Crangon; and a similar shrinking was observed in Pagurus 
by Paul Mayer. 
At the stage represented in fig. 8, all the Nauplius appen- 
dages have already become distinct. The optic plate has the 
form of a rounded lobe, distinctly marked off from the rest of 
the blastoderm behind, but passing gradually into it in front. 
The first antenne are larger than the other appendages, and 
are dilated at their extremities. Their preoral position is at 
this time unmistakable, the mouth appearing as a narrow 
trausversely elongated slit, bounded by closely-set nuclei, at 
the level of the interval between the first and second pairs of 
appendages. The second antennze and the mandibles are 
simple, rounded papille. The ventral plates have ceased to 
be prominent externally, though they are, as will be seen, 
easily recognised in section. The thoracico-abdominal rudi- 
ment has the form of a rounded papilla, projecting slightly 
from the posterior surface of the blastoderm, but connected 
with the cephalic region by an even slope. There is at this 
stage no sharp flexure of the posterior part of the embryo 
upon the head, such as is seen in the next stage. It need 
hardly be pointed out, that the existence of such a stage as 
that here described is quite incompatible with the formation 
of an abdominal flexure at an earlier period by the appear- 
ance of the epiblastic pit described by Kingsley. The nuclei 
of the whole post-oral region of the body exhibit a marked 
tendency towards an arrangement in parallel rows, lying 
