92 LIFE AND HABIT. 



The mammals lay eggs, which they hatch inside 

 their own bodies, instead of outside them ; but the 

 difference is one of degree and not of kind. In all 

 these cases how difficult is it to say where identity 

 begins or ends, or again where death begins or ends, 

 or where reproduction begins or ends. 



How small and unimportant is the difference 

 between the changes which a caterpillar undergoes 

 before becoming a moth, and those of a strobila before 

 becoming a medusa. Yet in the one case we say the 

 caterpillar does not die, but is changed (though, if the 

 various changes in its existence be produced metageneti- 

 cally, as is the case with many insects, it would appear 

 to make a clean sweep of every organ of its exist- 

 ence, and start de now, growing a head where its feet 

 were, and so on at least twice between its lives as 

 caterpillar and butterfly) ; in this case, however, w r e say 

 the caterpillar does not die, but is changed; being, 

 nevertheless, one personality with the moth, into which 

 it is developed. But in the case of the strobila we say 

 that it is not changed, but dies, and is no part of the 

 personality of the medusa. 



We say the egg becomes the caterpillar, not by the 

 death of the egg and birth of the caterpillar, but by 

 the ordinary process of nutrition and waste waste 

 and repair waste and repair continually. In like 

 manner we say the caterpillar becomes the chrysalis, 

 and the chrysalis the moth, not through the death of 

 either one or the other, but by the development of 

 the same creature, and the ordinary processes of waste 

 and repair. But the medusa after three or four cycles 



