180 Mr Sharp, Modification and attitude o/" Idolum diabolicum, etc. 



petaloid coloration is found on other Mantises in different parts 

 of the body and in /. diabolicum exists on a part in which pig- 

 mentation of a purposeless nature frequently occurs. 



On the other hand our comparative sketch of attitude and 

 movement shows that they must be looked on as of more 

 importance, and that they have probably preceded the modifica- 

 tions. In other words, that in the past the function of catching in 

 a particular manner has preceded the modifications of structure 

 for doing so. 



Herbert Spencer has argued 1 that " function is from beginning 

 to end the determining cause of structure." 



In the case of Idolum diabolicum we have seen that the habit 

 or instinct has preceded certain moditi cations. The modifications 

 may be described as the localisation and exaggeration of certain 

 phenomena that are of usual occurrence in Mantidae. And the 

 further question arises as to the aetiology of this localisation. It 

 would at present be rash to endeavour to answer this question ; 

 still I hope I may be permitted to say that I believe that this 

 localisation of modification will ultimately be found to be due 

 to the reactions between simple physical causes and the physio- 

 logical processes of the creature. 



Description of Plate. 



Idolum diabolicum, female, natural size. The plate is made by aid of 

 a dried specimen from Mozambique and of a coloured sketch of 

 the Insect during life by Mr Muir. The Insect is represented in 

 its favourite attitude ; the position during life is a matter of 

 indifference, and the creature may be either suspended or erect. 

 The tarsi of the front legs are broken in the specimen, and the 

 restoration of them attempted in the plate is bad, as they are 

 made to look like spines. 



1 Principles of Biology, 1st edition, Vol. i., p. 167. In the revised and enlarged 

 edition of 1898, p. 211, the words quoted are altered as follows : "the achievement 

 of function is, throughout, that for which structure arises." I think the original 

 mode of expression is preferable as being less teleological. 





