SECT. 6] 



OF THE EMBRYO 



895 



Figs, 232 and 235, the water-content of the whole system rising, that 

 of the yolk remaining steady and that of the embryo slightly falling 

 (82 to 75 per cent.). The total weight of this egg rises considerably, 

 from 76-9 to 132-8 mgm. and as will be shown later, ash as well as 

 water is absorbed during development. The undeveloped egg of 



15-0 



14-0 



13-0 



12-0- 



10-0- 



100 



Sepia contains 40-4 mgm. of water but the hatched embryo ioo-6 mgm. 

 so that 60 per cent, of the final amount must have been taken in from 

 the sea. The percentage of water in the system correspondingly rose 

 from 52-5 to 75-81. 



The work of Weismann indicated a similar absorption of water 

 during the embryogeny of the cladoceran, Daphnia, and this was con- 



1 An equation for the egg of the axolotl, Amblystoma, can be derived from Dempster's 

 data : 



Wet + External = Wet + Dry yolk used for 



yolk water axolotl other purposes 



(i-ogm.) (3-92 gm.) (4-84 gm.) (0086 gm.) 

 Ranzi's figures apply to the pre-hatching period only, Dempster's apply to the whole 

 yolk-sac period as well. 



