226 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 
of the future caudal bristles. In front of the end of the abdominal process, two minute 
conical prominences, at first marked by similar, but fewer clear striæ, gradually raise them- 
selves up on each side from the surface of the blastoderm and elongate, their apices being 
directed backwards. They are the rudiments of the antennules and antennæ. 
A delicate structureless membrane is now visible, covering these parts and the adjoining 
portions of the germinal membrane. It is produced into the terminal setæ of the end of 
the abdomen and of the two pairs of appendages, and is the commencement of the first 
skin of the larva*. 
The anterior part of the blastoderm is wider than the posterior, and is produced into 
two great lobes divided by a median fissure. These are the “ procephalic lobes," and have 
the same relation to the anterior division of the head as the corresponding parts in the 
embryo Aphis. 
In this state the embryo becomes a larva, for it bursts its vitelline envelope and lies 
naked in the pouch of the mother. The rudimentary abdomen is at the same time ex- 
tended, so that the little creature is now about 35th of an inch in length, and is very like 
a pear in shape, the stalk being represented by the abdomen, which is terminated by å 
flattened, bifid, spinulose fin. 
The whole larva is covered by a continuation of the delicate membrane already noticed 
on the limbs and abdomen. The blastoderm invests the abdomen almost completely, but 
in front it covers only a somewhat fiddle-shaped area on one face of the yelk. It is still 
more deeply bilobed in front, and the antennules and antennæ are much elongated. 
The larva next begins to grow, being doubtless nourished by the fluid contained in the 
maternal pouch; and at the same time its ventral region assumes a curve, contrary to 
that which it originally possessed, becoming more and more convex. 
The cephalic region is now clearly distinguishable; it occupies nearly one-half of the 
whole length of the body. The procephalic lobes extend upwards over the anterior face 
of the vitellus, and upon each a large rounded elevation, the rudiment of the ophthalmic 
peduncle, has made its appearance in front of the antennule. The latter, like the antennæ, 
elongate greatly, and become divided longitudinally, within the sheath afforded by the 
primitive integument, into their two terminal branches. 
Å slight constriction indicates the boundary between the antennulary and antennary 
sterna, and behind these, similar depressions mark off the surface of the blastoderm into 
seventeen additional segments. 
Attached to them are as many pairs of appendages, which in the youngest larve 
examined had the following form :— 
The first pair were rounded massive elevations, situated one on each side of the pit 
indicating the position of the oral aperture; from their anterior edge a short oval palp 
already projects. These are the rudimentary mandibles. 
The next pair, or first maxillæ, are small rounded elevations meeting in the middle line. 
The second maxillæ succeed, and are more elongated, three-jointed, and bent back parallel 
with one another. The maxillipedes and the thoracic ambulatory legs form one continuous 
* See, for illustrative figures of the development of Mysis, my ‘ Lectures’ above cited. 
