of the Fishery Board for Scotland. 81 
and are fringed on both edges of their distal halves with short, stout plain 
hairs. The exopodite overlaps the endopodite on the anterior side of the 
latter. In the third pair of pleopods of one larva there were 21 hairs on 
the exopodite, viz. 13 on the outer side, 2 terminal, and 6 on the inner 
side, 7.e. next the endopodite. The endopodite was somewhat smaller 
than the exopodite, and bore 19 hairs, viz. 3 terminal and 8 on each side. 
The endopodite extends as a continuation of the stem of the appendage. 
There is a variation in this stage which is common ; it is the case wherein 
the pleopod is furnished with rather longer fringing hairs, a proportion, 
larger or smaller, of which are sparsely plumose. The pleopods apparently 
function to a slight extent in this stage. 
The two forms observed of the third stage then are:—IIla, zoée 
having pleopods fringed with short plain hairs; IIIb, zoée having 
pleopods fringed with rather longer hairs, which are in part sparsely 
plumose (fig. 36, pl. ii.). It is possible that IIIb is the more common. 
This was the structure of the pleopod in the III. zoea stage described by 
Smith. 
The most striking secondary form is one which partakes of the 
characters of both zoéa and megalops. It will probably be more con- 
venient, then, to define the normal or average megalops before proceeding 
to discuss the intermediate variation. 
The zoéa has certain prominent characters ; these are the dorsal hooks 
on the abdomen, the purely maxillipede form of the pereiopods, the 
swimming exopodites of the thoracic appendages, and the stumpy 
antenne, which do not function as feelers. The pleopods in the zoéa are 
not fringed with long plumose setz. 
The megalops stage is marked by the antenne being long, minutely 
jointed, and used as feelers. The pereiopods function for walking ; the 
exopodites are greatly reduced. The pleopods are furnished with long, 
densely plumose sete, and have become powerful swimming organs. The 
dorsal hooks on the abdomen are absent. 
The intermediate stage, which is, for convenience, labelled thus “ IV.” 
in the plates, was quite common among the larvee that were reared. Fig. 
71, pl. iv., represents the most common condition of this form ; for it also 
varies. The antennule and the antenna are still not fully developed ; 
the former is single, and bears at its extremity a bunch of hairs. The 
antenna is longer than it is in Stage III.; it shows some segmentation, 
and coming joints are indicated externally by the presence of little hairs ; 
it is not a functional feeler. In other respects this form is a zoéa, The 
spine and hook armature of the abdomen is that of the zoéa. The 
pereiopods and their exopodites are in the zoéa condition. Drawings of 
the first pereiopod are given in figs. 43, 44, and 38, pl. ii. The part of 
the second protopodite joint which bears the exopodite is now segmented. 
The epipodite is also segmented off from the first protopodite joint (figs. 
44 and 38). The protopodite of the second pereiopod is represented in 
fig. 39, pl. ii. The endopodite has five joints—a chelate tip. 
It resembles a megalops in its pleopods, telson, and the hand of the 
first pereiopod. The pleopods are large, and fringed with long plumose 
sete. On the third pleopod (fig. 51, pl. ii.) there are on the exopodite 
33 sete, and on the endopodite 30 sete. The exopodite overlaps the 
endopodite on the anterior surface. The hand of the first pereiopod was 
long, at that of a megalops rather than that of the zoéa (fig. 43, 
pl. i1.). 
The Stage ‘‘ IV.” varies to the extent of having its pleopods furnished 
with comparatively short hairs, some of which at least are sparsely 
plumose. This is the condition found in the modification of the third 
stage zoéa, labelled IIIb. The largest specimens are usually furnished 
