MUSEUM OF COMPARATIVE ZOOLOGY. 311 
baling the water out from the branchial chamber before the least trace 
of the gills has appeared. As the currents of blood in the zo&a stream 
along the sides of the carapace, they are aérated through the delicate 
integument by the constant flow of water kept up by the movement of 
the scaphognathite, which thus plays the same part as in the gill- 
bearing adult. 
Next follow tho three pairs of maxillipeds, which, in tho early stages 
of development, serve as swimming-organs. The first pair is the smallest. 
Its basal segment (PL I. Fig. 17, VZ) has a strongly convex inner 
margin, which is beset with sete. This part of the limb acts as a jaw, 
while the rest of the limb is used for locomotion. In this the appendage 
recalls the structure of the limbs in the Merostomata. The inner branch 
is composed of one segment. The outer branch (Pl. I. Fig. 14) is 
obscurely divided into two segments, and is considerably longer than the 
inner branch. 
The second pair of maxillipeds (Pl. I. Fig. 14, V77) consist in like 
manner of a basal segment and two branches. The inner branch con- 
sists of three segments, of which the proximal and middle are of about 
equal length, the distal very short. The outer branch is longer than 
the inner, and is indistinctly divided into five or six segments. Of 
these the first and second are of equal length, and form together the 
bulk of the branch. The following segments are crowded together near 
the tip of the branch, and the lines of division between them can barely 
be discerned. 
The third pair of maxillipeds (Pl. I. Fig. 14, V7Z7) exceed the second 
pair in length, but have essentially the same structure. The second 
pair, again, aro longer than the first pair. The branches of all the max- 
illipeds are furnished with long setze. 
Behind the third pair of maxillipeds are seen the rudiments of the 
two following pairs of thoracic appendages (Pl. I. Figs. 14, 17, IX, X; 
Fig. 13). They are two-branched, each branch having the form of a 
simple sac, without trace of a division into segments.* 
There are as yet no traces of abdominal appendages.t 
* Du Cano (Ann. Nat. Hist., Vol. II. Pl, VI. Fig. 2. 1839) and Bobrotzky (op. cit., 
p. 204, Pl, V. Fig. 17) both represent the first larval stage of Palamon with the 
rudiments of the first three pairs of walking-feet in the form of simple sacs. Iam 
inclined to believe that a more careful dissection would have revealed, in both cases, 
the structure which I have found in Palemonetes vulgaris, viz. two pairs of double 
sacs. 
+ According to Króyer (Monografisk Fremstilling af Slægten Hippolyte's nordiske 
