of the Fishery Board for Scotland. 



81 



and arc 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, i.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: — Ilia, zoese 

 having pleopods fringed with short plain hairs ; III&, zoese having 

 pleopods fringed with rather longer hairs, which are in part sparsely 

 plumose (fig. 36, pi. ii.). It is possible that III& 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 zoea 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 zoea 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 

 antenna?, which do not function as feelers. The pleopods in the zoea are 

 not fringed with long plumose setse. 



The megalops stage is marked by the antennae 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 setse, 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 larvae that were reared. Fig. 

 71, pi. 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 zoea. The 

 spine and hook armature of the abdomen is that of the zoea. The 

 pereiopods and their exopodites are in the zoea condition. Drawings of 

 the first pereiopod are given in figs. 43, 44, and 38, pi. 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, pi. 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 

 setse. On the third pleopod (fig. 51, pi. ii.) there are on the exopodite 

 33 setse, and on the endopodite 30 setse. The exopodite overlaps the 

 endopodite on the anterior surface. The hand of the first pereiopod was 

 long, resembling that of a megalops rather than that of the zoea (fig. 43, 

 pi. ii.). 



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 zoea, labelled III&. The largest specimens are usually furnished 



