MUSEUM OF COMPARATIVE ZOOLOGY. 319 
sented by Fig. 15 of Plate IV. This was frequently taken in the hand- 
net free-swimming at the surface of the sea, Although but eight milli- 
metres long, the larva has acquired the form and almost every charac- 
ter of the adult prawn. 
Among the drawings of Crustacean larve made by Mr. Agassiz at 
Newport, which he has generously placed at my disposal, are some 
details of the structure of a larval stage of Palcmonetes vulgaris which 
happily fills in some measure the gap between the sixth larval stage and 
the adult form. This phase in the development I will designate as the 
Seventh Larval Stage (Pl. IV. Figs. 9 - 14). — There is no sketch of 
the general form of this stage among Mr. Agassiz’s drawings. The 
rostrum (Pl. IV. Fig. 9) is long and scymitar-shaped, with six teeth 
above and two bolow. Between the teeth of the dorsal side are hairs, 
as in the adult. The anterior third of the rostrum is destitute of teeth. 
The carapace is armed, moreover, with an antennal and a minute bran- 
chiostegal spine on each side. "The supra-orbital spino is reduced to ۵ 
mere rudiment, 
The natatory branch of the maxillipeds and legs (Pl. IV. Figs. 10, 11, 
13, r e) is reduced to a short style composed of one segment. In this 
we see an interesting transition state between the Schizopod and the 
Decapod leg. The inner branches of the first and second pair of max- 
illipeds have also diminished, and now consist of one and two segments 
respectively (Pl. IV. Figs. 10, 11). The segments of the internal 
branches of the chelipeds and ambulatory appendages are clearly seven 
in number. The last pair of thoracic legs (Pl. IV. Fig. 14) is of course 
without the external styliform appendage. 
The antenne, swimmerets, and telson are not represented in Mr. 
Agassiz’s figures, nor is the natural size indicated. 
Specimens in the sixth larval stage may measure cight millimetres 
from the tip of the rostrum to the tip of the telson. This is as long as 
specimens which have attained the adult form, such as is represented by 
Figure 15 of Plate IV. Hence I infer that but few stages interveno. 
It is highly probable, however, that the larva suffers one or two moults 
between tho seventh stage and the attainment of the shape of the adult 
prawn. 
Early Stage of the Adult Form (P1. IV. Fig. 15). — Although measuring 
only eight millimetres from the tip of the rostrum to the end of the 
telson, the prawn has now the true Decapod structure; although still 
a free-swimming surface-dweller. Every trace of the external swimming- 
branches of the five pairs of legs has vanished, and the structure is in 
