202 



CRUSTACEA. 



maxillary region (Fig. 96, s), fusing in the median line only at a 

 later stage. Although here, as in the Cladocera (Grobben), the two 

 halves of the shell at first develop separately, we must, nevertheless, 

 trace them back to an originally single dorsal shield, like that of Apus. 

 In the youngest larval stages of Limnetis (Fig. 97) observed by 

 Orube (No. 23), the shape of the body is very remarkable. In the 

 number and structure of the limbs, this larva agrees with the so-called 

 NaupUus of other Branchiopoda, but it is distinguished by a flat, 

 circular, and somewhat transversely broadened, dorsal shield. There 



fr 



Fig. 95.— Older (Cladocera-like) larval stage 

 of Estheria (after Claus). a', first, a", 

 second antenna ; d, intestine ; fr, frontal 

 sensory organ ; h, heart ; k, gills ; md, 

 mandible ; n, nervous sj-stem ; o, Nauplius 

 eye ; sd, sliell-gland. 



is a correspondingly large and 

 transversely broadened upper 

 lip on the ventral side. At 

 the anterior cephalic region there 

 are one unpaired and two paired 

 lateral conical projections. The flat 

 dorsal shield is replaced by a bivalve 

 shell only at a somewhat late stage. 

 Many very primitive features 

 have been retained in the condition 

 of the body among the numerous 

 As such we may assume the presence 

 of many body-segments, the comparatively homomorphic develop- 

 ment of the limbs, the origin of the antennal nerves from a pair of 

 ganglia lying in the oesophageal commissure, the presence of separate 

 ganglia in each maxillary segment, the ladder-like development of the 



forms of the Uranchiopoda. 



