15 



Aftrr spvotri hcurs the rlnrula pradunlly npttlpr, toward 

 the bettor apain ard f orally the ?r"ira3 rover entr ceare, 

 due tc the loss cf the oilia. lor a time of vr.ryi-p; lo-pth 

 after the P-iral -otior stors thr rlanula glider alorr or 

 the botton of the araariur. About forty-e:ipht hours after 

 the egjTS are laid the larva reaches the stage of develo-- 

 ir.ert ir v;hirh attrchrerit takes -lace. In rre-aratior for at- 

 tachrrrt the plarula rettles to the bettor, loses its cilia 

 ard ceases ite- rovererts. 



FCE!/ATIOr OF THE ECTODE?.;'. 



The forratio- of the ectoderr in Stcrrctcca a^icata is 

 siir-le ir ccr^rariso^ rith these species i'- v.'hich the segrer- 

 tatior of the egp is ur.eoual, rivirp rise to racroreres 

 ard ricrcmeres; ard i'^ which the ectoder^ is forr^ed by a 

 ra^id i'-'crease of the nicroreres a:xl overgrov;irr of the nacrc- 

 ireres by the rrrcess rf eribole. Ir Stoirotrca or the ether 

 hard the oleavare is equal and at the ccrrt^leticr. cf seg- 

 i^ertaticr the blastOT-eres have divided irtr cells of uri- 



