L-4KJ'Al PSl'SlOf.V. 



I ;o 



that it forms a con\'enient f:tiu-!:!in f.xy.i': with relation to 

 which the growth of neighbouring" strucnires. particularh' 

 that of the endostvle, can be detennined. 



The upper and lower limbs of the endostvle are inclined 

 to one another at an acute angle, and mav be said to form 

 two unequal sides of a triangle, the apex of which is 

 directed backwards between the rows of secondar\' and 

 the primary gill-clefts (,Fig. ~~'\ 



Between the two rows of slits on the right side of the 

 body tliere is a blood-vessel, representing the anterior 

 continuation of the sub-intestiwal vessel, which ends blindly 

 in front above the first primarx' slit. This is the future 

 ventral branchial arterx', with which we are already ac- 

 quainted. When its hnal situation m the mid-ventral line 

 below the endostvle is remembered, its position in the 

 larva high up on the right side, as in Fig. 74, will appear 

 very striking. 



The secondary slits now go on growing in sice, and the 

 priman" slits gradualh" tend to disappear entirel\- from the 

 right side until, as in Fig. 7S, only the original upper por- 



Fig- 7S. — Ar.tc-rior ponior. of !.-.r\"A Irom ri^r,: sivio, lo ^^.0'.v :;;e b-i.ck\\\ird. 

 irrowth 01 '.'r.e endostvle between fne yriman- and second.irv g:' '.-slits, i Ar:er 

 WiLLEV.l 



-'■..\ Sense-or^.in ot pn^or.\'. pit. tj . Firs: prinian" s.i;. :*;. Intern.!", opening 

 oi ciub-sh.ipc'd gLvnd. £. Endostyie /..-. Penpharvng-eai ciiiated band. 



