(30) 



plain that I caimot agree with Lont^charrips in hiy statement that 

 the septum is secondary. It must be adndtlsd, however, tiiat 

 the septinii between ti;e lobe and the collar is o-f'ten consider- 

 ably thinner thaii that between the collar auu tne trunk. if 

 1 h.ad net follov;ea its ori.-,in from the earliest stages by means 

 0^ sections in three different, planes, whole ri'ounts aiiCi live ma- 

 terial, I sliOuld not have been inclined to consider it, as I dOj 

 a primary and constant o •"^an o^ the larva. 



I had confidently expectea to find in the larva of the 

 sta<?e represented in ^ig. 24 some indication of tne mesentery 

 between the collar and the trunk, but I was disappointed, Al— 

 thougli the ciliated tract alon(, Yrtiich the tentacles are to 

 arise has made its appearance ana extends obliquely around the 

 body poDper of the larva, inaic at in^- a line just a little above 

 tne line o^ separation of the cavities of the trunk ana collar 

 in the older Actino tro cha^yet exaMnat ioii of sectioxiS does not 

 show the least si^^n o '^ tiie mese^^tery or its funaament. 



Ikeda (9) has found mesoderm cells connectinj^ ti.e nephrid- 

 ial canals with the splanchnic walls arid i.e thinks tney are 

 the first inaication of the septum between the collar ana 

 trunk cavities. I have not been able to find th.e pairea mas- 

 ses of "hypoblast cells" which Masteman( 16) says give rise to 

 the trunk cavities although it is true that I fbund mesoderm 



