No. 2.] ANURIDA MARITIMA. 263 
appendages between the antennae and the mandibles, as well 
as the faint outline of the rest of the germ band. Up to the 
stage figured in Fig. 42 the chief changes are in the clearer 
definition of the six abdominal segments, the appearance of 
the median unpaired labrum, and the indication of the procto- 
deal and stomodeal invaginations. The antennae have become 
undoubtedly three-jointed, with an indication of a fourth, and 
the precephalic organ has begun its process of elongation and 
degeneration (Fig. 42). The embryo still preserves its spheri- 
cal form, and stretching across between the ends of the appen- 
dages can be seen the last envelope formed (Figs. 42, 44, m.). 
Whether this is a true larval skin or is similar to the “ Blasto- 
dermhauten”’ already discussed is not clear, but it can best be 
seen after the appendages have appeared. It seems most likely 
that it is shed just at the beginning of the embryo formation; 
it passes round the embryo, and is frequently found attached 
to the ends of the precephalic organ. 
From this point a radical change of form takes place; a 
flexure of the embryo begins that results in crowding the 
mouth-parts together to form a definite head and folding the 
embryo upon itself. This greatly changes the points of refer- 
ence in regard to the precephalic organ: the head remains in 
about the same position, but the tail is drawn much farther 
away, and the embryo becomes restricted to less than one-half 
of the circumference of the egg, instead of extending over 
nearly the whole. At the same time there is a marked lateral 
flattening, so that the young animal is much narrower meas- 
ured from side to side than measured dorso-ventrally. Before 
the final stage of this process is reached, however, certain 
features of note have appeared. The most striking of these 
are shown in Figs. 43 and 45. Fig. 43 represents an embryo 
in which the ventral flexure has just begun, as shown in the 
side view of Fig. 43, a. The brain lobes, the protocerebrum, 
have clearly appeared, and their elongation into optic lobes is 
evident. The labrum, unpaired, and lying on the middle line, 
is seen just anterior to the stomodaeum. The antennae lie on 
each side of the future mouth, and are formed of three short, 
thick, and approximately equal joints. The three pairs of 
