SECT. 5] 



IN ONTOGENESIS 



797 



The independence of the environment which has been noticed in 

 fresh-water teleosts extends also to marine teleosts, where there is a 

 sharp contrast as against elasmobranchs. Dakin obtained the fol- 

 lowing values by direct freezing-point determinations : 



Sea water 



Egg-contents of Pleuronectes platessa 

 Adult blood of Pleuronectes platessa 

 Egg-contents of Scyllium canicula 

 Adult blood of Scyllium canicula 



AH 



-1-91 

 -0-70 



-0-75 

 -I -80 

 -I -go 



Fig. 187. 



This was in agreement with Bottazzi's well-known findings that the 

 osmotic pressure and salinity of teleostean blood was different from 

 the sea (though it varied with it), while the osmotic pressure and 

 sahnity of elasmobranch blood was the same as the sea. Death of 

 the plaice egg destroyed its osmotic independence. Thus the teleost 

 egg, floating in sea water of salinity 35 per cent., had an osmotic 

 pressure corresponding to a salinity of only 14 per cent.; corre- 

 spondingly it will develop perfectly well in a mixture of 80 per cent, 

 fresh and 20 per cent, salt water. With regard to Scyllium eggs, Dakin 



