162 Part II. —Twenty-first Annual Report 
('p. Cunningham’s* description of the early young stages of Cancer 
pagurus. In this form also the carapace of the early crab stages is 
longer than broad. 
2. (Fig. 173). The carapace is now approaching the adult shape. 
‘It is slightly broader than long. The shortening of the carapace 
results in pushing out the toothed area on either side. 
The broad frontal region still persists. 
The minute cilia are still present on the carapace. 
3. (Fig. 170). The lateral teeth are a little farther out. The hind- 
most tooth now projects considerably beyond the level of the corner of 
the orbit. The frontal region is still very broad, and it shows the 
trilobed waving. 
The lateral teeth are gradually becoming of one size. 
Tbe ‘“‘needle-point ” cilia are seen on the carapace. 
The carapace is considerably broader than long. 
4. (Fig. 171). The lateral toothed border is now distinctly farther 
forward than in the previous stage. The frontal region remains prac- 
tically unchanged. 
The ‘“needle-point”’ cilia are still present. 
In the cast measuring 4°25 mm. of Waddington’s series, No. 1, p. 165, 
the “needle-point” cilia were not made out, but little tubercles were 
seen scattered over the dorsum of the carapace. 
Cras 5°5 mm. across (Fig. 172). In this specimen not much change 
in shape is noticed. The lateral teeth are now nearly all of one size. 
The minute cilia were not made out in this specimen. 
Aputt.—The change from the last crab to the adult condition (Fig. 
168, male, natural size) is a gradual lessening of the breadth of the 
frontal region, and a pushing forward of the toothed border into an 
antero-lateral position. The reduction in breadth of the frontal region 
is accompanied by the emphasising of the trilobed waving into three 
distinct lobes; the median projects a little in front of the other two. 
The tri-lobed frontal region develops by the gradual pushing out of 
the central lobe (rostrum). In the series of casts of No. 1 of 
Waddington’s collection (p. 165) the change in the frontal region is 
well shown. In the cast measuring 7:5 mm. across, the rostrum is seen 
to project very slightly in front of the broad frontal region. The three 
lobes are not distinct in this series until a size of 18 mm. is reached. 
Tn this stage the three lobes are well marked, but the lateral lobes are 
not so sharply cut off from the edge of the orbit as in the adult stages. 
THORAX. 
In the I. Zoéa (Fig. 85) the thorax appears in two distinct parts— 
the anterior narrow portion which bears the first and second maxillipedes, 
and the posterior part bearing the buds of the third maxillipede and the 
pereiopods. Its sternal surface is oval in shape, and it may be 
separated off, from the buds surrounding it, as an oval plate. In this stage 
it forms a comparatively small part of the sternum of the cephalothorax. 
During the remaining Zoéa stages it increases in size with the 
growth of the buds of the appendages, but even in the IV. Zoéa it does 
not yet bear its true proportion to the rest of the body: segmentation 
may be traced in it (Fig. 150). 
In the Megalops (Fig. 149) the part of the thorax that has developed 
during the Zoéa period, now forms the greater part of the sternum of 
the cephalothorax. Although the abdomen is not tucked up under the 
thorax, the latter is depressed posteriorly along the median line. 
* Cunningham, ‘‘ On the early post-larval stages of the common crab ( Cancer pagurus ), 
and on the aftinity of that species with Atelecyclus heterodon.” Proc. Zool. Socy. Lond., 
Mar. 1898, 1 pl. 
