474 



CRUSTACEA MALACOSTRACA. 



description (1780) of a member of the order. A dagger-shaped 

 telson projecting beyond the sixth segment, may or may not 

 be present. The anterior antennae are short and biramous. 

 The posterior are uniramous, short and, in many cases, unseg- 

 mented in the female, while in the male a multiarticulate flagellum 

 beset with sensory hairs and equalling the body in length is borne 



on a five- jointed shaft of the appendage. 

 The mandible is without a palp. The 

 two-lobed first maxilla has a back- 

 wardly directed process bearing two 

 long setae, which lie in the respiratory 

 chamber, in which feature, as in the 

 elongation of the posterior antennae of 

 the male, the Cumacea resemble the 

 Leptostraca. The second maxilla is a 

 small lobed plate. 



The first maxilliped of the Cumacea 

 (Fig. 293) is modified in relation with 

 a peculiar form of respiratory apparatus 

 ~ pf which finds its parallel only among the 

 Tanaidacea (see p. 478). The main 

 ramus is a short and stout setose limb, 

 in apposition with its fellow. From its 

 basal segment a large scoop-shaped 

 appendage (pp) projects upward and 

 backward into the respiratory chamber, 

 bearing on its inner margin a number 

 of branchial lamellae, which lie in the 

 hollow enclosed between the appendage 

 and the thoracic wall. Further, from 

 the base of the maxilliped another pro- 

 cess (ap) extends forward, which curves 

 round to meet its fellow in front of the labrum under the 

 front of the head, and with the adjoining parts, forms a 

 channel through which water, driven by the scoop-shaped plate, 

 is directed forwards from the branchial chamber. It would 

 appear that these processes must be regarded as epipodites. 

 The posterior, in the combination of branchial filaments with 

 a plate-like lobe, recalls the podobranchia of Astacus. Other 

 branchial structures are absent in the Cumacea. 



'IG 293 Right first maxilliped 

 of Diastylis stygia seen from 

 above (after Sars). a.p. an- 

 terior and p.p. posterior pro- 

 cess from the base of the ap- 

 pendage ; end basal segment 

 bearing the endopodite. 



