440 CRUSTACEA MALACOSTRACA. 



the thorax in which the eggs are contained and the young 

 develop.* 



In the Branchiopoda we have seen that the number of epipo- 

 dites of the thoracic legs varies from one to three, and there is 

 evidence of a corresponding variability in number in the 

 Malacostraca, though the homology of the epipodial structures 

 in the several orders remains to be elucidated. 



In the holotrophous Schizopoda the highly subdivided gill 

 apparently represents one epipodite, the oostegite apparently 

 represents another, and a rudimentary appendage described by 

 Sars in Gnathophausia (p. 465) is perhaps a vestige of a third. 

 It is to be noted that though in both Hemitropha and Holo- 

 tropha the majority of the gills, when present, have assumed a 

 highly complex form, that of the first thoracic leg in the Holo- 

 tropha retains the simple condition met with in Anaspides and 

 the Amphipods. 



In the Decapods four separate branchiae may be present in 

 relation with each thoracic limb (Fig. 317). They are inserted (1) 

 on the coxopodite (podobranchiae) and the gill filaments then 

 often spring from the surface of an epipodial plate, (2) on the 

 arthrodial membrane intervening between the coxopodite and 

 the thorax (arthrobranchiae), and (3) from the surface of the 

 thorax above the insertion of the appendage (one ortwopleuro- 

 branchiae). But, although so attached in the adult the pleuro- 

 branchiae are seen to spring in the larva from the bases of the 

 limbs (Glaus), and the branchiae are probably all to be regarded 

 as originally epipodial in origin (Fig. 317). The five anterior 

 thoracic legs of the Stomatopoda bear each a simple epipodial 

 lobe on the basal segment. 



The condition of the gills of the Laemodipoda (Amphipoda) is 

 remarkable in that some of the thoracic segments have lost all 

 other trace of appendages, but the gills (epipodia) remain, 

 attached to their ventral surfaces. 



The .uniformity which exists throughout the series of the 

 thoracic legs in the lower Malacostraca is modified in varying 

 degrees in the more differentiated groups by the adaptation of 

 one or more of the anterior members as maxillipeds, to subserve, 



* There are, however, among the Isopoda, instances of the formation 

 of a ventral brood pouch by structures, the relation of which to epipodial 

 oostegites appears remote and has not been made out. 



