MUSEUM OF COMPARATIVE ZOOLOGY. 259 
son, and on the lower side of the cephalo-thorax, There is also vermilion in 
the wall of the intestine. 
A few specimens were collected in a younger stage than that described above. 
They were somewhat smaller than the other specimens; the first pair of 
antennc were simple; with three or four sensory threads at the tip; the 
Decapodal legs were very small buds, much more rudimentary than in the 
later stage ; the third pair of maxillipeds were also smaller, with the inner 
branch much shorter in proportion to the outer branch; the four pairs of 
abdominal limbs were present, but of smaller dimensions ; the telson displayed 
but ten plumose seteo on its posterior margin. In other respects they agreed 
pretty closely with the older individuals. 
Many of the specimens in my aquaria developed from the oldest zoéa-stage 
directly into the first stage of the crab (Plate III. Fig. 1), described further 
on, in which there is not the slightest trace left of the rostrum or posterior 
spines of the zoéa. In one instance I detected the young crab in the very act 
of disengaging itself from its zoéa-case. In another young crab which had just 
emerged from the zoéa, the shrivelled remnant of the artery and other soft 
parts within the rostrum of the zoéa was still sticking to its front. 
Fritz Müller was right, then, when he surmised that the oldest Porcellana 
zoéa observed. by him at Santa Catharina (which was in the same stage as the 
oldest zoéa described above) would pass through the next moult into a form 
not differing essentially from the adult Porcellana,* although Claus thinks it 
probable that there is an intervening form corresponding to the youngest 
megalopa-stage of the Brachyura.t 
First Porcellana-stage (Plate ITI. Figs. 1-10). The carapace is now about 
2 mm. long ; its breadth is about the same as its length. It is suborbicular in 
its outline, the front broad and furnished with minute hairs. 
* Dio Verwandlung der Porcellanen. Arch. f. Naturgeschichte, 1862, 1, p. 198. 
T After describing the same stage as the oldest ono observed by Müller, Claus says: 
“Ueber die späteren Entwicklungsstadien fehlen mir leider Beobachtungen, doch 
wird es nach Analogie mit der Krabbenmetamorphose wahrscheinlich, dass sich noch 
ein Zwischenglied, etwa dem jüngsten Megalopastadium entsprechend, einschiebt. 
Fr. Müller bemerkt zwar, dass das mit der nächsten Hüutung hervorgehende Thier 
kaum wesentlich von der erwachsenen Porcellana verschieden sei, da die Porcellanen 
auf die Stufe der Megalopa stehen geblieben sind, Indess ist dabei zu bemerken, 
dass es sich hier um das Endglied der Megalopaformen handelt, zu welchem auch bei 
den Krabben die Zoéa nicht unmittelbar, sondern durch Zwischenformen führt." 
(Untersuchungen, p. 59.) In reality, one sees in the young Porcellana no zoda- 
characters persisting in the shape of large eyes, form and armature of the carapace, 
such as are found in the youngest stages of megalopw. In these regards it is as far 
removed from the youngest megalopa-stage as the adult is. The abdomen, moreover, 
is relatively no larger than in the mature animal, and, as far as I observed, but little 
used as a swimming-organ. True, the abdomen is furnished with two-branched 
setiferous appendages (Pl. IIT. Fig. 10), but this is not a peculiarity of the youngest 
megalopa-stage of Brachyura ; as wil be seen further on in Pinniwa, like appen- 
dages are retained (in both sexes, apparently), even in the youngest crab-stagos. 
