(20) 



Mcttit.eriaan (16) inveatigatea. nnly tiiat f o rt ion of t'.c v;all of 

 the ^ixstrula v/hich forms tiie outiiiK^ cf the blastopore is cap- 

 able of a.ivin;.: rise to luesoaerm ii. Piioronis architect a ana as 

 in the form studieci by LoiiticLamps (12), the aixterior and later- 

 al borders of tne blastopore are rnost active in this process, 

 (^igs. 16(a) (b) (c) (d) (e) (f) ) Most of tne mesoaerm is prolif- 

 erated from the aiiterior eiid of the arch evit eron, and the power 



of r>"oduciriij the same seerrs to diminish gradually towara the 



in 

 poste'-ior end of the blastopore lips those gaatrulae v/here the 



round blastopore is just beginnin,, to close up. (Figs . 16( a) (b) 



(c)(d)(e)(f) ) 



The mesoderm cells are very amoeboid in character and are 

 often seen in living specimens and sometimes iii sections send- 

 ini-, out long pseudopod-like prolongations v^i.icii become attached 

 to the walls of the gastn?la. Ey means of these afi:ioeboid move- 

 ments, they are able to crav/l up the walls o ^ the blastocoel. 



1 was urable to make out any structure jn Pn^ ".n" o archi- 

 tect a v;nich I could interpret as "archei.te ric diverticula" such 

 as fignjred by Caid./^ii (3a) and Ikeda (9), ■Pig.i6(c) ndght 

 be inter^.'-etoa us showing these diverticula but the condition 

 there is hardly different from the arrangement of the mesoderm 

 c .xj-s ..nlch are being pustiea out into the blastocoel in front 

 '^f the blastopore. (^igs. 16-16(b) ) Caldwell first observea 



