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 

 antennae 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 setce 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 zoea-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 zoea. In one instance I detected the yoimg crab in the very act 

 of disengaging itself from its zoea-case. In another young crab Avliich had just 

 emerged from the zoea, the shrivelled remnant of the artery and other soft 

 parts within the rostrum of the zoea was still sticking to its front. 



Fritz Muller was right, then, when he surmised that the oldest Porcellana 

 zoea observed by him at Santa Catharina (which was in the same stage as the 

 oldest zoea described above) would pass through the next moult into a form 

 not differing essentially from the adult Porcellana* although Claus thinks it 

 probaljle that there is an intervening form corresponding to the yoimgest 

 megalopa-stage of the Brachyura.f 



First Porcellana-stegfe (Plate III. 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. 



* Die Verwandlung der rorcellanen. Arch. f. Natnrgeschichte, 1862, 1, p. 198. 



t After describing the same stage as the oldest one observed by Muller, Claus says: 

 " Ueber die spateren Entwicklungsstadien fehlen mir leider Beobachtungen, doch 

 wird es nach Analogie mit der Krabbenmetamorphose wahrscheinlich, dass sich noch 

 ein Zwischenglied, etwa dem jiingsten Megalopastadium entsprechend, einschiebt. 

 Fr. Miillcr bemerkt zwar, dass das mit der nachsten Hiiutung hervorgehende Thier 

 kaum wesentlicli von der erwachsenen Porcellana verschicden sei, da die Porcellanen 

 auf die Stufe der Megalopa stehen gohlieben sind. Indess ist dabei zu bemerken, 

 dass es sich hier um das Endglied der Megalopaformen handelt, zu welchem aiich bei 

 den Krabben die Zoea nicht unniittelbar, sondern durch Zwischenformen fuhrt." 

 (Uiitersuchungen, p. 59.) In reality, one sees in the young Porcellana no zoea- 

 characters persisting in the shape of large eyes, form and armature of the carapace, 

 such as are found in the youngest stages of megalopoe. 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 (PI. III. Fig. 10), but this is not a peculiarity of the youngest 

 megalopa-stage of Brachyura ; as will be seen further on in Pinnixa, like appen- 

 dages are retained (in both sexes, apparently), even in the youngest crab-stages. 



