Chap. YII. ZOE^ OF MACRURA. 55 



setae. As in tlie Crabs, there are only two pairs of 

 well-developed natatory feet (maxillipedes), but tbe 

 third pair is also present in the form of a two-jointed 

 stump of considerable size, although still destitute of 

 setae. The tail bears five pairs of setae. The little 

 animal usually holds itself extended straight in the 

 water, with the head directed downwards. 



This is also the position in which we usually see the 

 Zoeae of the Shrimps and Prawns (fig. 27), which agree 

 in their general appearance with those of the Hermit 

 Crabs. Between the large compound eyes there is in 

 them a small median eye. The inner antennae bear, at 

 the end of a basal joint sometimes of considerable length, 

 on the inside a plumose seta, which also occurs in the 

 Hermit Crabs, and on the outside a short terminal joint 

 with one or more olfactory filaments. The outer 

 antennae exhibit a well-developed and sometimes dis- 

 tinctly articulated scale, and within this usually a spini- 

 form process ; the flagellum appears generally to be still 

 wanting. The tliird pair of maxillipedes seems to be 

 always present, at least in the form of considerable 

 rudiments. The spatuliform caudal lamina bears from 

 five to six pairs of setae on its hinder margin. 



The development of the Zoea-brood to the sexually 

 mature animal was traced by Spence Bate in Carcinus 

 masnas. He proved that the metamorphosis is a per- 

 fectly gradual one, and that no sharply separated stages 

 of development, like the caterpillar and pupa of the 

 Lepidoptera, could be defined in it. Unfortunate] 

 possess only this single complete series of obs^rvatkks * L 



