570 



<'i.\ss II. ONvrimi'linitA. 



hind end of I In- hlastopore (Ki^ r - .'Ml />'). This elongation of 

 I In- emhryo is accompanied hy n.n elon^at ion of the hlastopore, 

 uhieh soon hecomes diimh hell shaped ( Ki^. .'M4 C}. At the 

 same lime I he mesohlasl ie somites (emhryonie -se-j incuts of 

 mesoderm) have made t heir a ppearance in pairs at the hind end, 

 and iM-adually travel forward on each side of the hlasloporc 

 to the front end, where the somites of the anterior pair soon 



meet in front of the blastopore (Ki.u. .'Ml />). Meanwhile the 



narrow middle part of the hlastopore has closed hy a fusion 



I'M. ::il \scric of embryos of /'. O//WM.V/X 'I ltd hind oiul of oiubryos U, C, D is upper- 



si, 111 the ll-Hirs, III,- pIllilllHe lleal. I. Ill,- ulllle |,:ilrli lirliilnl III.- I ,l:i : I < ' | MV (after 



of its lips, so that the blastopore is represented by two 

 openings, the future mouth and anus. A primitive groove 

 makes its appearance behind the blastopore (Fig. 344 D). At 

 this stage the hind end of the body becomes curved vent rally 

 into a spiral (Fig. 344 E), and at the same time the appendages 



appear as hollou processes of the hody wall, a mesohlasl ic somite 

 heiiij prolonged into each of them. 'I'he lirst to appear are the 



antennae, into which the praeoral somites are prolonged. The 



remainder appear from before hackuards in regular order, vi/. 

 jaws, oral papillae, legs 1-17. The full number of somites and 



their appendages is not, ho\\ever, completed until a Interstate. 

 The nervous system is formed as an annular thickening of eelo 



