cealment, or hiding. Yet, notwithstanding these 

 devices and the enormous prolificacy that obtained, 

 the balance of life was maintained at a critical 

 point. In this mighty struggle for existence, the 

 welfare of many species was entirely dependent on 

 some feature of form or color. 



Still, even these devices in numerous cases were 

 not sufficient to enable their possessors to hold 

 their own in the stifling competition that raged 

 along the shore ; and many of these were crowded 

 into the deeper regions or took to these of their 

 own accord; the rest became extinct. 



That the spider-crab is such an exile, is only too 

 plain. Its masking habit clearly indicates its ori- 

 gin. This habit, now useless, arises from an in- 

 stinct, a reflex, inherited from ancestors who, liv- 

 ing under conditions quite dissimilar, doubtless 

 then derived from it a direct advantage. 



IV 



The foregoing experiments were carried out in 

 a somewhat desultory manner during the summer 

 months succeeding the discovery of these remark- 

 able creatures on the occasion of the nocturnal 

 episode described in the preceding chapter. How- 



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