I'MI:N i OF mi: PWO MII.J.I.K r,; | 



111 



iriittit/tkftin'' in to bed' 



,-,)i (Darmdrtisenblati > 



Tin- succeedim: prooessea of development have as their ob 

 point the detachment From one another, by mi .and 



fu>ion, of the parts \\hich are still in cont inuii y. and tin* torn... 

 of discrete cavities. The process's of constriction heiri- 

 anterior end of tin- embryo, and progress tlience to the bl;i-i 

 (liu r s. To au<l 71). At first the lutly -;tt-s become deeper (tiir. 7u ///), 



- J/i 



Fig. 71. -Cross section through an Amphioxus emhryo with five well-developed primitive seg- 

 ments, :in.-r HATSCHEK. 

 at, Outer, it-, inner, ink; niiildle germ l:i\i-i ; ),/', ineilullarv i>l;it<- ; eft , chorda ; dh, intestinal 



i\ ity. 



Fig. 72. -Cross section through the middle of the body of an Amphioxus embryo with clever 



primitive segments, after H.vrsriiK.K. 

 ;;, Neural tube; us, primitive segment. F.-r "f the other letters see Fig. 71. 



and tlu'ii lost'tht-ir cmuici-t ion \vitli tlio main cavity (////) Itythe close 

 appo-iiioii of the cells \vhie-h Mirround tin- mtramvs to tlit-in (1'iL 1 '. 

 r.y this proc- th- iiiai'irin of the secondary iMitodfrni (//.') OOmi 

 abut directly on the margin of the chorda! fun / //). The 



latt.-r has lut-ainvhile also und"ri::i' rhan.ir's ; the plate-like fu 

 iinMit lias become SO curved by tin 1 elevation -t' it> lateral mar 

 that there has arisen a d e;> chordal \\ Inch is open alon. 



ventral side. Subsequently the lateral \\alU < t the groove come into 

 close contact . and are tln'reby onvert-d into a -"lid n 1 of cells, which 

 teni|)rarily >hai'e> in the rlosure .f the roof of the secondary intestine. 

 and aj.j>rar> ftSj a rid.u'e-like thickening of the latt. 

 rod (c/<) becomes detache.l (ti_i:. 7_) from the wall of the intestine ; the 

 latter now. for the first time, becomes completely closed in the form 

 of a *mbe. To effect this the margii entodenn, indicated in 



