ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 
417 
side of the median line as far back as to the segment bearing 
the first pair of maxillae. These give out short branches to 
the mandibles. 
At a little later stage than the last, a short spine-like process 
(fig. 70, d.s.) becomes visible on the dorsal median line of the 
carapace. This is the rudimentary dorsal spine, which so com- 
monly occurs in the Crab Zoea. At the posterior end of the 
yolk-mass, where it joins the proctodaeum, small vacuoles and 
oil drops (figs. 70 and 71, lv.), both of very refractive appear- 
ance, appear. I have not clearly followed the development of 
these vacuoles and oil drops, but I am inclined to consider them 
as the first indication of the liver. 
The heart (figs. 70, 71, h .) now appears on the dorsal aspect 
of the embryo within the mesodermic cells occupying the 
position just outside the place where the liver (?) globules have 
appeared. I have not obtained any good section which shows 
the origin of the heart, but my observations tend to show that 
it is mesodermic in its origin. The pigment of the eye is now 
seen for the first time in this stage. 
More segments come into view, and at the stage represented 
in figs. 72 and 73, the segments posterior to the last pair of 
maxillipedes have increased up to ten. 
The first pair of antennae {At. 1) now shows a slight con- 
striction on its sides, thus marking out the future basal and 
the proximal portions. 
The second pair of antennae [At. 2) which is as long as the 
first pair, shows the future flagellum and the scale, the latter 
considerably broader than the former, and beset with a number 
of short setae on its upper side. The flagellum is bifurcated 
at its tip. 
The mandible (figs. 72, 73, md .) shows no definite structure 
as yet. 
The first and the second pairs of maxillae and the first pair 
of maxillipedes (figs. 72 and 73, mac. 1, 2, mocp. 1) have consi- 
derably changed. They all show traces of the future lobules on 
their inner sides. The exopodite of the first pair of maxillae is 
furnished with three short points, while those of the second 
