58 



finally v/ith the -ri^ratinr endodprrr cells. Wher the develOD- 

 in.r Pf^g is r.bout six tc eight hours old, the very irreg- 

 ular sharDe, which the seg:renting rass has assumed, becomes 

 less marked. Gradually the cells becore rearranged; the 

 lobes a-^d processes which rreviously were so conspicuous 

 are now drav/n into the nain mass of cells, and the egg is 

 transformed into an oval e-bryo. This ^Fccecs of rounding 

 uri lasts fro-- two to four hours. The cells of the erbryo 

 now develori cilia, and the larva begins to rove. At first 

 the riovements are feeble, but soon the larva is able to 

 leave the bottor. of the aquariun and svar, free in the water. 

 Eggs that are laid at five to six o'clock in the norning 

 develop to the free-swir.r,ing stage by four in the afternoon. 

 The larva sv/ins with its broad end forv/ard! and has v. 

 snaal or cork-screw notion, which proreis it onv/ard. 

 This "lethod of swinning is con^on tc hydroid larvae. When 

 the embryo reaches this stage the cells become very nuir.er- 

 o~us and snail. And before the cilia are developed and 



