156 Part IIL.—Twenty-jirst Annual Report 
The continuity between the cavity of the limb and that of the gill is 
well seen in this stage. 
III. (Fig. 74). The gill of the chela is now double. 
IV. (Figs. 67 and 79). The separation of the limb into its basal part 
(pleuron, ap) and the limb proper has taken place, and the gills of the 
pereiopods are, although not yet functional, now large, and show their 
relation to the limb proper. 
The epipodite and two gills of the third maxillipede are well 
developed. 
The process on the second maxillipede which was noticed on the 
I. Zoéa is now prominent (Figs. 66, 67, and 174). It represents 
probably the epipodite and one gill. 
Mecatops (Figs. 80, 64, and 86).—The gills connected with the 
pereiopods are now functional, and they occupy the positions they do in 
the adult. The twoarthrobranchs of the chela are attached to a space 
between the pleuron and the coxopodite, a-br (2); in the case of the 
second and third pereiopods the pleurobranch is attached to a circular 
opening in the pleuron (pl-br, Fig. 80.) 
On the second maxillipede (Fig. 64) the gill and epipodite are attached 
to the first joint of the protopodite. They both rise from the same 
stem. The gill is a podobranch, and is yet unsegmented. The second 
gill, viz. the arthrobranch, which is found attached to this appendage in 
the adult was, if present, not noticed. 
On the third maxillipede (Fig. 86) three gills are found in this stage, 
none of which are segmented. Two are arthrobranchs; they are the 
gills present in the Zoéa stages. There is also a small gill attached to 
the second protopodite joint close to the origin of the epipodite ; it and 
the epipodite are probably developed from the long epipodite process 
seen in the Zoéa, 
1. The podobranch of the second maxillipede (dr, Fig. 71) shows 
some segmentation in its proximal part. A second plain gill (67 7) was 
made out in one case. The gills are very liable to be knocked off in 
dissection, and unless the maxillipedes are separated from one another 
the relations of the parts are not satisfactorily made out. 
On the third maxillipede (Fig. 88) only one of the gills is divided into 
lobes—viz., the larger arthrobranch. The other arthrobranch and the 
little podobranch have still the smooth outline. 
In my paper on the larval stages of Crangon vulgaris it was stated, 
with reference to the gills of the pereiopods, that starting from the 
podobranch condition they passed through an arthrobranch (non- 
functional) stage (V.) and that in the Megalops (V1.stage) they appear 
as functional gills (pleurobranchs) for the first time. Re-examination 
of these stages has shown that the interpretation of the developing gill 
in the V. stage as an arthrobranch is wrong. In that stage it is a 
pleurobranch. 
The description given above of the epipodites and gills shows a close 
similarity between them in their origin and development. This is 
especially the case in the second and third maxillipedes, where a 
podobranch and an epipodite are apparently derived from the one bud. 
The development of the epipodite of the first maxillipede is included 
in the description of that appendage, p. 148. 
(TABLE. 
