CHAP. VII. ZOEA-BROOD. 49 



seem likewise to commence their lives as Zoeae : 

 witness the Porcettanse, the Tatuira (Hippa emerita) and 

 the Hermit Crabs. Among the Macrura we are ac- 

 quainted with the same earliest form principally in 

 several Shrimps and Prawns, such as Crangon (Du 

 Cane), Caridina (Joly), Hippolyte, Palcemon, Alpheus, 

 &c. Lastly, it is not improbable, that the youngest 

 brood of the Mantis-Shrimps (Squilla) is also in the 

 same case. 



The most important peculiarities which distinguish 

 this Zoea-brood from the adult animal, are as fol- 

 lows : 



The middle-body with its appendages, those five pairs 

 of feet to which these animals owe their name of Deca- 

 poda, is either entirely wanting, or scarcely indicated ; 

 the abdomen and tail are destitute of appendages, and 

 the latter consists of a single piece. The mandibles, as in 

 the Insecta, have no palpi. The maxillipedes, of which 

 the third pair is often still wanting, are not yet brought 

 into the service of the mouth, but appear in the form 

 of biramose natatory feet. Branchiae are wanting, or 

 where their first rudiments may be detected as small 

 verruciform prominences, these are dense cell-masses, 

 through which the blood does not yet flow, and which 

 therefore have nothing to do with respiration. An in- 

 terchange of the gases of the water and blood may occur 

 all over the thin-skinned surface of the body ; but the 



towards their dwelling places, which are reached only by a few." For 

 what purpose would be these destructive migrations in species whose 

 young quit the egg and the mother as terrestrial animals ? 



E 



