GENERAL CHAEACTERS. 7 



anterior {h, i, k, I), and in some genera the fifth (m,) pairs 

 of limbs, these plates are much larger than in the three 

 or two posterior pairs ; but to compensate for this diminu- 

 tion of size, the three posterior {7n, n, o), with few generic 

 exceptions, have the second joint produced posteriorly 

 into a large and squamiform plate. In Caprella and the 

 allied genera, the first joint of each leg is fused with the 

 body of the animal, and is never shaped like scales. 



The five posterior pairs of legs (pereiopoda, k-o) are 

 the walking appendages ; they homologize with the ten 

 legs in the Decapoda, and as efi^ciently fulfil their design. 

 Like them, they consist of seven joints ; but, unlike 

 them, all articulate in planes vertical to the body of 

 the animal, having no lateral movements. The two ante- 

 rior pairs of walking legs are directed forwards, and the 

 three posterior are directed backwards. Thus the seven 

 pairs of legs constitute three distinct series, generally 

 differing from each other in their proportions, size, and 

 direction, the first and second pairs being subcheliferous, 

 the third and fourth porrected, and the fifth, sixth, and 

 seventh pairs directed backwards. 



The branchiae (i") consist of a series of vesicles ; a 

 single sac being attached to, and pendent from, the first 

 joint of all the legs except the first, and in the males of 

 some genera also the last. 



The ova are nurtured within a pouch formed by a 

 series of foliaceous plates (i'"), one of which is attached 

 to the first joint of the four anterior pairs of legs in 

 females. In this pouch the embryo continues until it 

 has arrived at a period when there is but a slight dis- 

 tinction in form between it and the parent, except in 

 the Hyperina, as has been shown by Milne-Edwards 

 and Gossej where the form of the young animal differs 

 considerably from that of the parent. 



Posterior to the legs used for walking, are three pairs 



