254 BULLETIN OF THE 
reached on either side ; the three following interspaces contain two denticles ; 
the wider space between the outer spine on either side and the lateral tooth 
gives room for four denticles. Thus we have thirty-nine denticles in all, in 
place of about one hundred in the stage described by Smith as the second. 
There is no vestige of appendages upon any of the abdominal segments. 
The first pair of antenne (Plate I. Fig. 8) are nearly as in the earliest stage 
as described by Smith ; but in some specimens I detected the rudiment of 
the secondary flagellum in the shape of a small tubercle at their base (a). On 
this point, however, there may be some doubt, as the secondary piece does not 
appear, according to Mr. Smith’s observations, until the megalopa-stage is 
reached. 
In the second pair of antenne (Plate I. Fig. 9) the rounded prominence 
which represents the rudimentary flagellum in the “second ” stage of the zoéa 
is so slightly developed as to be scarcely discernible (c). 
The labrum (Plate I. Fig. 6 a) is enormously developed, and seems to be 
almost prehensile when one watches the motions of the living animal. The 
oral appendages and the first and second pairs of maxillipeds (natatory legs) 
(Plate I. Figs. 5, 6, 10-12) are similar in structure to those of the youngest 
stage observed by Professor Smith ; the outer lobe of the first pair of maxilla 
(Plate I. Fig. 11 0); however, has but two slender teeth instead of three, as in 
the later stage, and the outer branches of the natatory legs (Plate I. Figs. 5, 6) 
bear four long plumose sete instead of eight. Other differences will be most 
readily seen by comparing my figures with Professor Smith's. There is no 
trace of any appendages back of the second maxillipeds, 
Length, including the abdomen, about 1 mm, 
The heart is plainly visible through the transparent carapace, on the dorsal 
side of the cephalo-thorax. It has the form of a large, irregular pentagon, lying 
within a lozenge-shaped pericardial sac, with which it is connected by six 
delicate threads. The pericardium itself is attached to the walls of the body 
by stronger ligaments. 
The heart gives off three arteries. Of these, one proceeds from the anterior 
angle, in the median line of the body, in the shape of a large tube to the base 
of the rostrum, where it suddenly diminishes in volume, but persists as a very 
minute canal to the tip of the rostrum. At the base of the rostrum, just where 
the diminution of the median artery occurs, a large lateral tube is given off on 
each side, which convey the bulk of the blood from the median channel to the 
eye-stalks, These arteries, which might be appropriately termed the rostral 
and ophthalmic arteries, are together equivalent to the ophthalmic artery of the 
adult, the small terminal branches to the eyes in the adult being here found in 
the form of long and capacious vessels, in relation to the large size of the eyes 
and their distance apart in the larva. 
From the posterior part of the heart, two arteries are given off in the middle 
line of the body. The upper one is small, extends backward through the 
abdomen on the dorsal side, and ends in the telson. The other has its origin 
at nearly the same point as the first, but plunges down to the lower face of 
