II 



CARAPACE OF CLADOCERA 



39 



iu Ceriodaphnia. In a few forms the whole surface is irregularly 

 covered with spines or scales. The hinder edge of the carapace 

 is often produced into a median dorsal spine (Daplinia, Fig. 19), 

 or more rarely there are two spines, one at each ventro-lateral 

 corner (Scapholeberis, Fig. 20). 



The cuticle of the carapace is often separated from that of 

 the head by a cervical suture, as in Simoceplialus (Fig. 10, C.X.\ 

 and near the line of demarcation many forms exhibit patches of 



c.s. 



FlG. 10. fiinKici'ji/i/ift'x i-i-tiilna, X 30. Siilc view of female, .showing the arrangement 

 of the principal orpins. A. 2, Second antenna ; C.S, cervical suture; /,'. fused 

 compound eyes ; //, heart : L, forwanlly-directcd i;astne caeca ; T, dorsal organ. 



glandular ectoderm which seem to be homologous with I In- 

 dorsal adhesive organs of the Limnadiidae. Tlie commonest 

 condition is that of a median dorsal pit 'Fig. 10, JV.\ by means 

 of which the animal can fix itself to foreign objects. Certain 

 forms may remain for long periods of time attached by 1 In- 

 dorsal organ to plants, or to the sides of an aquarium, the onl\ 

 movement being a slow vibration of the feet, l>y \\hich a current 

 of water, sullieiently rapid for iv-piratory purposes, is rsi,iMi:-hcd 

 round it. 1 In Xulu crystallina (Fig. 11) the dorsal or-an is 

 represented by three structures ; in front there is a median raised 



1 SiiiiiH'i'/i//,t/iis f'/ II /UK anchors itself to \\eeds, etc., liy ,l inoililie.l 3eta "ii tlir 



exopodite of the second antenna. It does not employ a dorsal orjrm fur pnr|'' 

 of fixation. [G. S.] 



