172 



are very similar to the Hist zoea in appearance. Between 

 the two branches of the antenna an outgrowth takes place 

 in the second stages, and ultimately developes into the 

 long flagellum. The maxillae are not very different from 

 those of the first stage. The setae on tlie exopodites of the 

 first and second maxillipedes increase in number at every 

 stage. The last six pairs of thoracic appendages and 

 their gills gradually increase in size, but never become 

 functional during the zoea stages. The pleopods 

 gradually develop until at the fourth stage there are five 

 pairs present. There is not a pair present on the sixth 

 abdominal somite in Carcinus. At the third stage the 

 sixth abdominal somite becomes separate from the telson. 

 The rostral and dorsal spines gradually become shorter. 



In his account of the larval stages of Cancer irroratus, 

 Smith describes the following characters in the last zoea 

 stage: — Rostral and dorsal spines short. The abdominal 

 legs are seen as stumpy outgrowths. The third niaxilli- 

 pede is well developed, but the other posterior thoracic 

 appendages do not project below the edge of the cephalo- 

 thoracic shield. The flagellum of the antenna is present. 



Megalopa stage. The main points of difference 

 between the zoea and megalopa are as follows: — The 

 frontal and lateral spines disappear. According to 

 Smith, the dorsal spine of Cancer irroratus persists as a 

 small backwar dry-projecting process. The carapace is 

 broader. The pereiopods are well developed, and the 

 gills are probably functional. The pereiopods are never 

 biramose as in the Macrura. The abdomen is macrurous, 

 and the pleopods are used for swimming. The telson is 

 much shorter, and loses its spines. The megalopa is still 

 a pelagic stage. Its pereiopods, however, may be used for 



' Smith, S. " The Invertebrate Fauna of Vineyard Sound," U. S. 

 Fiali Commission Report, 1871-72 (published 1873). 



