SIMILAR INSTINCTS IN UNALLIED ANIMALS. 27^ 



CHAPTER XVIII. 



Instinct (continued). 



Cases of Special Difficulty with Eegard to the Fore- 

 going Theory of the Origin and Development of 

 Instincts. 



We must not take leave of Instinct without looking into all 

 the known cases of its exhibition which admit of being 

 reasonably cited against the views here expressed on the rise 

 and development of instincts generally. I shall therefore 

 consider seriatim all such cases which I have met with in the 

 writings of others, or which occur to me as admitting of being 

 po iibly cited in this connection. 



Similar Instincts in Unallicd Animals. 



Mi\ Darwin observes in the Appendix, " We occasionally 

 meet with the same peculiar instinct in animals widely 

 remote in the Bcale of nature, and which consequently cannot 

 have derived the peculiarity from community of descent." 

 The difficulty, of course, is to account for the parallelism, and 

 the instances given by Mr. Darwin are those of the Molothrua 

 having the same instinct of parasitism as the Cuckoo, the 



Termites having much the same instincts as the Ants, and a 



neuropterous and a dipterous larva having the same instinct 

 of digging a pitfall for prey. He shows satisfactorily that 

 : I b-mentioned is the only case that offers any real diffi- 

 culty ; but even here, it Beema to me, the difficulty is not one 

 of any magnitude For the instinct in question is not one 

 of such complexity, or of such remote probability as to its 

 formation where a larva habitually lives in sand, that we 

 may nol readily believe a similarity of environment should 

 have determined its development independently in two lines 



