582 



ZOOLOGY 



SECT. 



presence of a carapace which leaves some of the posterior 

 thoracic segments free and in the number both of segments 

 and appendages, but present several interesting characters 



Th. 8 



^V% 



FIG. 458. Paranaspides lacustris, x4. a 1 , antennules ; a 2 , antennse ; Ab. 1, first 

 abdominal segment : ep, epipodites or gills on the thoracic legs ; md, mandible ; Pl.l, first 

 abdominal appendage ; T, telson ; Th.fi, eighth free thoracic segment ; U, uropod. (After 

 Geoffrey Smith.) 



indicating a lower grade of organisation. One of the most 

 notable of these is the absence of differentiation in the thoracic 

 appendages, which, though they have a leg-like and not a leaf-like 

 form, are all alike, none of them being modified into maxillipedes, 



FIG. 459. Mysis oculata. end. endopodite; c.>: exopodite ; ot. otocyst. (After Gerstaecker.) 



except to a very slight degree in some forms. Moreover, the legs 

 all possess exopodites (ex), thus retaining the primitive biramous or 

 " split-footed " form which is lost in the Decapoda. The first five 

 pleopods are large in the male, small in the female: the sixth 



