176 LIFE AND HABIT. 



contemplation. Ten or a dozen should, I think, be 

 sufficient for the future. 



As regards plants, we read : 



" Hybridised embryos probably often perish in like 

 manner. ... of which fact Max "Wichura has given 

 some striking cases with hybrid willows. ... It may 

 be here worth noticing, that in some cases of parthano- 

 genesis, the embryos within the eggs of silk moths, 

 which have not been fertilised, pass through their early 

 stages of development, and then perish like the embryos 

 produced by a cross between distinct species " (Ibid). 



This last fact would at first sight seem to make against 

 me, but we must consider that the presence of a double 

 memory, provided it be not too conflicting, would be a 

 part of the experience of the silk moth's egg, which 

 might be then as fatally puzzled by the monotony of 

 a single memory as it would be by two memories which 

 were not sufficiently like each other. So that failure 

 here must be referred to the utter absence of that 

 little internal stimulant of slightly conflicting memory 

 which the creature has always hitherto experienced, 

 and without which it fails to recognise itself. In either 

 case, then, whether with hybrids or in cases of partheno- 

 genesis, the early death of the embryo is due to ina- 

 bility to recollect, owing to a fault in the chain of 

 associated ideas. All the facts here given are an excel- 

 lent illustration of the principle, elsewhere insisted upon 

 by Mr. Darwin, that any great and sudden change of 

 surroundings has a tendency to induce sterility; on 

 which head he writes ("Plants and Animals under 

 Domestication," vol. ii. p. 143, ed. 1875) : 



