SECT. 5] 



IN ONTOGENESIS 



807 



solutions to an extent just sufficient to keep the product of the 

 equation constant, but the sea-urchin's eggs did not do this. Fig, 194 

 shows on curve A the actual behaviour of the eggs, volume being 

 plotted against osmotic pressure of external medium, and B the 

 theoretical curve which should have resulted if the Boyle-Mariotte 

 law had been followed. It is evident that the divergence is greatest 

 in very hypotonic solutions, nil in normal sea water, and again 



+10 



+ 9 - 



+ 8 - 



E ^7 



I- 



> +5 

 CT) +4 



"> .3 



C 



~ +2 



C 



O +1 



3 4 5 6 7 8 9 10111213 

 pH 



Fig. 193. A. Strongylocentrotus. B. Sabellaria. 



marked in hypertonic solutions. In other words, the sea-urchin's 

 egg opposes a certain amount of resistance to extreme hydration on 

 the one hand, and to extreme dehydration on the other. Ephrussi 

 & Neukomm offered no explanation for these facts, but thought 

 it as difficult to picture any considerable amount of glucose getting 

 into the Qgg from hypertonic solutions as to picture any electrolytes 

 passing out in hypotonic solutions. If Fig. 194 be compared with 

 Fig. 190, the difference between the polychaete and the echinoderm 

 egg as regards the Boyle-Marriotte law will easily be seen. 



