THE CRUSTACEA 125 



indeed, by due care, the antennae of the pupa may be always 

 detected ; the posterior extremity is directed vertically upwards. 



" The larvae in the first stage have three pairs of legs, a very 

 simple single eye, and a probosciformed mouth, with which 

 they feed largely, for they increase much in size. In the second 

 stage, answering to the chrysalis stage of butterflies, they have 

 six pairs of beautifully constructed natatory legs, a pair of magni- 

 ficent compound eyes, and extremely complex antenna ; but they 

 have a closed and imperfect mouth, and cannot feed ; their function 

 at this stage is to search by their well-developed organs of sense, 

 and to reach by their active powers of swimming, a proper place 

 on which to become attached and to undergo their final meta- 

 morphosis. When this is completed they are fixed for life : their 

 legs are now converted into prehensile organs ; they again obtain 

 a well-constructed mouth ; but they have no antennae, and their 

 two eyes are now reconverted into a minute, single, and very 

 simple eye-spot." 



The King-Crabs (Xiphosura) and the Sea-Spiders (Pycnogonida), 

 formerly associated with the Crustacea, are now regarded as more 

 closely related to the Arachnida. 



