of the Fishery Board for Scotland. 



153 



III. (Fig. 74). The buds have grown rapidly. There is an indica- 

 tion of a basal joint being segmented off on the cliela. In one example 

 also the dactylopodite was segmented off on the chela. 



IV. (Figs. 67, 79, and 82). The pereiopods are now segmented. The 

 first joint consists of the proximal part, i.e. the future pleuron. The 

 jointing is distal to the gills in the first three pereiopods (Figs. 67 and 

 79). Beyond that there are five segments. The pereiopod is divided 

 into six joints, in which the first becomes the pleuron {ap^ ib.), and the 

 remaining five joints form the adult pereiopod. The complete segmen- 

 tage into six joints was not found in every lY. Zoea, e.g. in Fig. 82 only 

 five joints were made out. 



Megalops (Figs. 89, 90, 93, 95, 105, 106). In this stage all the 

 pereiopods are functional. The 6-jointed state of the previous stage is 

 now replaced by a 7 -jointed condition, in which the first joint is the 

 pleuron, and the remaining six form the walking limb, the joints being 

 the coxopodite (cox), basi-ischiopodite (b-isch), meropodite (mer), carpo- 

 podite {ca7y), propodite {prop), and dactylopodite (dact), Fig. 90. The 

 basi-ischiopodite is so named from the view that it represents the union 

 of the basiopodite and ischiopodite joints of the walking limb of the 

 Macrouran.* It is interesting that no such union is shown in its 

 development. Instead of any reduction taking place in the number of 

 joints, the resulting number is the maximum amount of segmentation 

 through which the limb passes. It is probable that the basi-ischiopodite 

 joint is segmented off from the third joint in the IV. Zoea (i.e., counting 

 the pleuron as the first joint). 



The pereiopods in the Megalops have certain characters which belong 

 to this stage and which vanish in the next stage. These consist in a 

 large hook on the distal part of the basi-ischiopodite of the chela, short 

 toothed spines on the dactylopodite (and propodite) of the second, third, 

 and fourth pereiopods, and the long curved spines which so well 

 characterise the dactylopodite of the fifth pereiopod. 



The drawings of the 1-5 pereiopods — viz. Figs. 106, 95, 93, 89, and 

 105 respectively — do not show the whole limb, but simply that part distal 

 to the fracture plane, which occupies the same position as in the adult, 

 (on the proximal part of the basi-ischiopodite). The differences between 

 the limbs are found on these parts. Fig. 90, however, shows the com- 

 plete fifth pereiopod, and Fig. 101 is an enlarged drawing of the 

 coxopodite and basi-ischiopodite joints. There is little difference to 

 remark between the coxopodites of the pereiopods except that of size 

 (Fig. 149, PI. xii.). In the preserved specimen the limb breaks off 

 readily at the fracture plane : this is especially the case where the 

 Megalops or young crab has been killed in the preserving fluid. 



All the limbs are well furnished with smooth hairs. The coxopodites 

 have a few hairs, which are usually plumose (Fig. 101). 



1st Pereiopod (Fig. 106). The first pereiopod is a functional chela. 

 The basi-ischiopodite joint is expanded at its distal inner border into a 

 strong curved hollow hook. Spread over the different joints are 

 the short hairs shown in the sketch ; the propodite and dactylopodite 

 are profusely supplied with these (Fig. 109). Along either side of the 

 " knife-blades " are three (or two) of the short stiff curved hairs which 

 were found in a similar situation on the chela of the VI. (Megalops) 

 stage of Crangon vulgaris. The knife-blades are crossed by what 

 appear to be little tubes ; a bundle of these is seen in the claw termina- 

 tion of each jaw. In connection with similar tubes found in the chela 

 of Crangon, it was suggested that possibly by these a lubricant of soma 



* Leon Fredericq. 



