THE BRANCHIOPODA 



33 



a. 



hep. 



The carapace may be directly continuous in front with the 

 dorsal integument of the head as in most Cladocera, or defined 

 from it by a groove as in some Cladocera and the Notostraca. In 

 the Conchostraca the con- 

 nection between the animal 

 and the shell is reduced to 

 a comparatively narrow neck 

 and the lateral lobes of the 

 shell extend forwards on each 

 side so as to enclose the 

 whole head (Fig. 17). Gener- 

 ally the shell-fold does not 

 coalesce with any of the 

 trunk-somites which it en- 

 velops, with the exception 

 of the one or two anterior 

 somites which in the Clado- 

 cera are fused with the head. 

 In the aberrant Cladoceran 

 Leptodora, however, it coal- 

 esces with the dorsal surface 

 of the leg-bearing somites, 

 and its free portion, which 

 here, as in some other Clado- 

 cera, forms merely a brood- 

 sac, appears to arise from 



the posterior margin of the ft - c . brood-chamber; br, brain; c, margin of carapace; 



, r , . /TT ., ~x c.s, caudal setae; e. compound eyes coalesced into 



Sixth trunk-SOmite (Fig. 19). one;/, furca; gl, maxillary gland; h, heart; hep, 



rrn i__ hepatic diverticulum of gut ; n.e, nauplius eye ; ov t 



ihe carapace may be ov y> (A fterCiausandGrobbeii.) 

 more or less corneous, but 



it is never strongly calcined. In a few Cladocera (Monospilus, 

 etc.) and in the Conchostraca (Fig. 17) the integument of the 

 outer surface of the shell is not cast off in ecdysis, but remains 

 in position, giving rise to a series of " lines of growth " marking 

 the increased size of the shell at each moult. Special modifica- 

 tions of the carapace for protection of the eggs will be referred 

 to below. 



The number of trunk-somites varies very much. It is greatest 

 in the Notostraca, where 42 somites are found in certain 

 species of Apus. In the Conchostraca the number is from about 

 13 to 28, and in the Anostraca 19 to 23. In the Cladocera the 

 segmentation of the body is generally more or less obscured ; at 

 least the first two somites are always coalesced with the head. In 

 Daphnia, according to Claus, these are followed by three limb- 

 bearing somites, and the succeeding apodous region is divided in 

 the young into three " abdominal " somites and a " postabdomen " 



autennule ; , antenna ; 



