17 



tc ir.ultiDnlar mif^rcitirT^. l>^ the rultirc\ir fcrratior of 

 the rr^doderr he distinruiEhec four different nodes, nare- 

 ly: 1. A rri-ary delarrinatior v,-hich takes rlace by a trars- 

 verse diviricr of the blasted err cells, and occurs ir the 

 Geryoridae ard Eudepdriuir . ?., A irultv-clar inpression 

 ;vhich takes ci all sides ( Aepinc-sis) . 3. /. secondary de- 

 la-inatio" -vhich occurs v/here a rrrula structure exists, as in 

 ;^£lliyra, i'hcralcrera ard in irort of the hydro id rolyns. 

 4. A irixed delairiraticr i' vhich the endodernal cells orig^ir- 

 ate ir rart throuph transverse divisicr or i'^Fressior; ard, 

 also, thrcuFh subsecuent differer tlaticr as a secondary 

 dela-iration. This last rode of the fcrTratio- of the eelc- 

 drr-r, accordinp to : etschrlkoff , occurs in Fplyxenia; and 

 is the transitional ^^ethod between Triultinolar nitration 

 a:^d enibole. In the urirclar ingression, cr "hynctrone" nrc- 

 ccss the for~atio" of the endoderr is confined tc a rc- 

 naratively snail arer at the nrstrrior end of -he blastula. 

 This is the irethod that is follov-od ir the species under 



