ON THE ZOiEA OF CARDISOMA ARMATUM. 11 



2. A Note on the Zoasa o£ a Land-Crab, Cardisoma armatum. 

 By H. Graham Cannon, B.A., F.Z.S. 



[Received October 24, 1922 : Read March 6, 1923.] 

 (Text-figures 1-6.) 



Among the Land-Crabs it is known that the females of the 

 genera Gecarcoidea and Gecarcinus resort to the sea in order that 

 the young aquatic larvse, on hatching from the eggs, may swim 

 away into the water. According to Moreira [1912] ripe females 

 of Cardisoma guanhumi also resort to salt or brackish water for 

 this purpose, whereas, according to Caiman [1909j, neither 

 Ortmann nor Andrews observed any specimens of the Cardisoma 

 Mrtipes in the neighbourhood of the sea. 



During September 1922 a female land-crab of the species 

 G. aronatum Herklots, kept in captivity in the Society's Gardens, 

 was noticed to be carrying a large mass of eggs underneath the 

 abdomen. The eggs proved, on examination, to be fertile, and in 

 a late stage of development. It was obviously of interest to find 

 out whether the eggs of this species would hatch in fresh or in 

 salt water. 



Some eggs were removed fi-om the female and placed in pure 

 artificial sea-water, while others were placed in tap-water. A 

 third lot were put into brackish water made of equal parts of sea- 

 water and tap-water. The next day all the eggs appeared healthy, 

 and the embryos in most showed a fairly regular heart-beat. 

 After two days those eggs in the tap-water had become opaque, 

 more especially in the central part of the egg, while those in 

 brackish water and sea-water appeared to be developing normally. 

 After three d:^ys many of the sea-water eggs hatched out and the 

 young appeared quite vigorous. In the brackish water only a 

 few hatched out, but these also appeared quite healthy. In the 

 fresh water some of the eggs had burst the shell, but the young 

 had disintegrated. It appears very probable from this that 

 C. armatum also resorts to the sea, or at least to brackish water 

 for spawning-purposes. 



The larvse only survived a few days after hatching and did not 

 develop further, although they were being ofiered the diatom 

 Nitzschia as food. It could not be seen whether the larvae were 

 actually taking the diatoms into their stomachs. 



The larvae were typical Brachyuran zoaeae. The frontal spine 

 slopes downwards and then curves upwards, and ends by re- 

 curving down again (text-fig. 1). There is a pair of lateral spines 

 projecting outwards and slightly forwards (text-fig. 2). All the 

 spines of the carapace are simple. The antennae are very simple 



