160 Part I11.—Twenty-first Annual Report 
The Tetson (Figs. 151 and 158) now functions simply as the shield of 
the anus. It has not yet adopted the adult form; in the latter the 
telson is of a triangular form, with a more or less pointed apex. ‘The 
telson may be raised from the thorax independently of the abdomen. 
In this stage the dorsal surface is provided with ciliated hairs, and it is 
also covered with the minute surface cilia. 
The Preopops (Figs. 145 and 156) have degenerated in this stage. 
Tn absolute measurement, although the crab itself has increased greatly 
in size, they are smaller than the pleopods of the Megalops. The 
abdomen now being closely fitted into the hollowed surface of the 
thorax, they can no longer function as swimming organs, and they have 
not yet taken on their adult sexual form. They are devoid of sete and 
hooks (Fig. 156) ; one or two minute hairs are seen on the exopodites. 
The fact that the endopodite is merely a process of the basal joint, not 
a separate branch, is well seen in this stage. 
The fifth pleopod (Fig. 156) is a small shrunken process, in which the 
separation into two joints is not always visible. 
2. In the second young stage the pleopods are similar to those of the 
first young stage, but smaller. 
External Sexual Characters. 
Inthe second young stage the external sexual characters have not 
appeared, I have not followed the development of the pleopods farther 
by successive stages, but the swimmerets of the female and the penes 
of the male appear very soon after the second stage. The breadth of 
carapace in the latter is about 2°5 mm. 
Ina crab measuring 5; mm. across the greatest breadth of the cara- 
pace, the female sexual characters were found. The swimmerets were 
present in their adult form, consisting of a 1-jointed exopodite and a 
2-jointed endopodite (Fig. 165). Neither branch bore any hairs at all. 
The position of the vulvze, viz. in the twelfth somite, that to which the 
third pereiopod belongs, was indicated by little clear depressions, but 
there were no openings. In a female 9 mm. across, the vulve were 
small clear circles (apparently not yet perforated); the swimmerets 
resembled those of the adult female, but very few hairs were present on 
each branch. 
In a crab measuring 54 mm. across (greatest breadth of carapace), the 
male sexual characters were found. The two penes were present, the 
anterior (1 p) and the posterior (2 ), Fig. 155. No trace of vulvee was 
seen in this specimen. The tubercles on the eleventh somite were 
prominent. A small clear area, not very distinctly made out, was 
noticed on the coxopodite of the fifth pereiopod, in the situation occupied 
in the adult by the external opening of the vas deferens. 
No distinction in the breadth of the abdomen which separates the 
adult sexes was yet apparent. 
THE Eyes, 0, 
I. (Figs. 159, 161, 163). The eye of the I. Zoéa resembles that of 
Crangon vulgaris * in that its cornea is a specialised portion of the 
carapace. Drawings of the moulted carapace of the first Zoéa are 
shown ; oblique side view Fig. 161, and ventral view 163. ‘The cornea 
is labelled, o. 
The median eye was not made out, although an irregular black area 
was seen in the region where the median eye was to be sought for. 
* Op. cit. 
