34 



THE CRUSTACEA 



or telson. This segmentation of the apodous region is distinctly 

 retained in the adult Leptodora (Fig. 19). 



Apart from the presence or absence of appendages, the trunk of 

 the Branchiopoda is not differentiated into distinct regions. By 

 various authors the terms "thorax" and "abdomen" have been ap- 

 plied respectively, sometimes to the pre- and post-genital, sometimes 

 to the limb-bearing and limbless regions of the trunk. As the 

 limits between these regions do not coincide, even approximately, 



r-f. 



FIG. 19. 



teptodora Tdndtii, female, x 10. ', antennule ; ", antenna ; c, carapace, reduced to a brood- 

 sac ; c.s, caudal setae (compare figure of Daphnia, p. 33) ; e, compound eye ; /, furca ; p, first 

 trunk-limb. (After Lilljeborg.) 



except in the Anostraca, it seems better to avoid altogether the use 

 of the terms " thoracic " and " abdominal " in dealing Avith this 

 group. 



In the Notostraca a varying number (4-14) of the posterior 

 somites are without appendages. In the post-genital region of the 

 body the number of pairs of appendages greatly exceeds the number 

 of somites, some of the posterior somites carrying as many as six 

 pairs. In the Anostraca there are from four to nine limbless 

 somites, but at least the two anterior are coalesced to form the 

 genital segment. In the Conchostraca the short post-pedal region 

 is unsegmented. 



