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 antennae (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 fiagellum 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 antennae (Plate I. Fig. 9) the rounded prominence 

 which represents the rudimentary fiagellum in the " second " stage of the zoea 

 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 maxillae 

 (Plate I. Fig. 11 6), 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 setae 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 



