OF CATERPILLARS 265 



well be true that the association of the ants with the 

 caterpillars has escaped notice ; or, on the other 

 hand, that in these instances the glands secrete a 

 fluid which has no saccharine ingredients. The 

 advantage that it may be to the caterpillar to se- 

 crete a sweet fluid attractive to ants is obvious, 

 since the ants undoubtedly keep off many iclmeu- 

 mon flies and other enemies of the caterpillar, and 

 the mutual benefit conferred by ant and caterpil- 

 lar is unquestionable. It is doubtful if in the 

 other cases the gland ever secretes a fluid having an 

 offensive quality which might equally serve as a 

 protection against intruders, since this means of 

 defense is probably found, in caterpillars of this 

 group, in organs of a very different character upon 

 the succeeding abdominal segment, and it is hardly 

 to be presumed that two organs, distinct in their 

 position and structure, should arise in one and the 

 same animal for precisely the same object. The 

 use, therefore, of the median gland presumably not 

 possessing a saccharine character is very problem- 

 atical. 



It should not be overlooked in connection with 

 this subject that these caterpillars are themselves 

 fond of saccharine matters. They, and only they, of 

 all our butterfly caterpillars, attack flowers where 



