486 STOMATOPODA. 



(2) The three last maxillipeds develop before the abdominal feet, as 

 biramous appendages, but subsequently completely atrophy, and then sprout 

 out again in their permanent form. 



(3) The abdominal feet develop in succession from before backwards, 

 and the whole series of them is fully formed before a trace of the appendages 

 of the three hindermost thoracic segments has appeared. It may be 

 mentioned as a point of some importance that the Zoaea of Squilla has 

 an elongated many-chambered heart, and not the short compact heart 

 usually found in the Zoasa. 



The younger stages of the Alima larva are not known 1 , but the earliest 

 stage observed is remarkable for presenting no trace of the three posterior 

 pairs of maxillipeds, or of the three following pairs of thoracic appendages. 

 The segments belonging to these appendages are however well developed. 

 The tail has its full complement of segments with the normal number of 

 well developed swimming feet. The larva represents in fact the stage of 

 the Erichthus larva when the three posterior pairs of maxillipeds have 

 undergone atrophy ; but it is probable that these appendages never become 

 developed in this form of larva. 



Apart from the above peculiarities the Alima form of larva closely 

 resembles the Erichthus form. 



Nebaliadae. The development of Nebalia is abbreviated, but from 

 MetschnikorPs figures 2 may be seen to resemble closely that of Mysis. 

 The abdomen has comparatively little yolk, and is bent over the ventral 

 surface of the thorax. There is in the egg a Nauplius stage with three 

 appendages, and subsequently a stage with the Zoaea appendages. 



The larva when it leaves the egg has the majority of its appendages 

 formed, but is still enveloped in a larval skin, and like Mysis bends its 

 abdomen towards the dorsal side. When the larva is finally hatched it does 

 not differ greatly from the adult. 



Cumaceae. The development of the Cumacece takes place for the 

 most part within the egg, and has been shewn by Uohrn (No. 496) to 

 resemble in many points that of the Isopods. A dorsal organ is present, 

 and a fold is formed immediately behind this which gives to the embryo a 

 dorsal flexure. Both of these features are eminently characteristic of the 

 Isopoda. 



The formation of the two pairs of antennas, mandibles, and two pairs 

 of maxillae and the following seven pairs of appendages takes place very 

 early. The pair of appendages behind the second maxilla; assumes an 

 ambulatory form, and exhibits a Schizopod character very early, differing 

 in both these respects from the homologous appendages in the Isopoda. 

 The cephalo-thoracic shield commences to be formed when the appendages 

 are still quite rudimentary as a pair of folds in the maxillary region. The 



1 The observations of Brooks (No. 493) render it probable that the Alima larva 

 leaves the egg in a form not very dissimilar to the youngest known larva. 

 a His paper is unfortunately in Russian. 



