132 EXTERNAL FACTORS III. 8 



the effects of this substance are due to its inhibition of 

 oxidation ; that this is the real cause of the prolongation of 

 the life of the eggs is shown by the fact that when kept in 

 an atmosphere of hydrogen for thirty-eight hours they were 

 still capable of being fertilized and developing into swimming 

 larvae. 



TABLE XVII 



Showing the effect of exposures of various length of Sea-urchin 

 eggs to a solution of KCN 57^ (After Loeh.) 



Lengtli of exposure in hours. 



Result. 



'I 



66 



90 



99 



112 



120 



139 



140 



161 



168 



80 % Plutei, vitelline membrane formed 



30 % Plutei, no vitelline membrane formed 



20 % Plutei, 



Less than 20 % Plutei 



Gastrulae, but no Plutei 



A few blastulae 



Blastulae, not swimming 



Eight-celled stage only 



Simultaneous lowering of the temperature to the freezing-point 

 enhanced the value of the cyanide treatment. 



In later stages, however, immediately after fertilization and 

 subsequently, the action of potassium cyanide is by no means 

 beneficial ; at this time, as we know, oxygen is a necessity (see 

 above, p. 112); and Lyon has shown that the moment at 

 which the ova are particularly sensitive to both KCN and 

 the lack of oxygen is the same, about fifteen minutes after 

 insemination. 



Chemical agents are also able to incite irregularities of growth 

 and abnormalities in later stages of development. 



In a long series of experiments Fere has shown that mon- 

 strosities can be produced by exposing the Hen's egg to the 

 unfavourable influence of a large variety of substances. Vapours 

 of ether, alcohol, essential oils, nicotine, mercury, and phosphorus, 

 injections of alkaloids such as morphine, nicotine, strychnine, and 

 others, of bacterial toxines (those of tubercle, diphtheria), of 

 peptones, dextrose, glycerine, several alcohols, certain salts (KBr, 



