CRABS AND SHRIMPS. 



181 



Another peculiarity is, that there seems to be but one 

 pair of legs, which terminate each in a hooked spine. 

 You now and then see these awkwardly thrust out from 

 beneath the hinder part of the shell, but locomotion is 

 principally effected by the pencilled antennae. There is, 

 however, a second pair of legs, but these do not usually 

 make their appearance outside the shell, being curved 

 backwards to sustain the ovaries. 



v\\ 



sJy 



CTPRIS. 



Early in the present century, an Irish naturalist, Dr. J. 

 Vaughan Thompson, announced a discovery, which, up- 

 setting conclusions previously received by all, caused no 

 little dissent and opposition, and gave rise to a lengthened 

 and wide-spread controversy. A very minute crustaceous 

 animal was known as inhabiting the open sea, to which 

 the name of Zoea had been given. It had sessile (i.e., not 

 stalked) eyes, and was remarkable for having a long spine 

 projecting from the face, and a similar one standing up 

 from the centre of the back. Another form was known, 

 which constituted the genus Megalopa ; in which the 

 body was broad, the eyes stalked, and the abdomen pro- 

 jecting behind. This was also small, but somewhat 

 larger than the preceding. 



Xobody suspected that these were other than inde- 



