Structure of Scent Organs in Male Danaine Butterflies. 175 



olfactory organs, and further that such odours can be 

 definitely associated with wing-brands, tufts, scales, and 

 other specialised portions of the anatomy of these insects. 

 In the case of the Danaine brushes and brands we can have 

 no doubt as to the function, or the association of that 

 function with sexual purposes. Throughout the animal 

 kingdom we are familiar with an infinite variety of elaborate 

 devices providing for the continuance of the species, and 

 in insects the olfactory sense seems pre-eminently chosen 

 as the agent whereby the species may attract and find its 

 mate. Perhaps the most remarkable feature of the organs 

 here described is the elaborate development of friable hairs 

 producing quantities of dust which almost certainly plays 

 a very important part in the distribution of the scent, 

 an interpretation strongly supported by the observed 

 behaviour of A. psyttalea, and it is further remarkable that 

 the dust may arise from either the brush or the wing 

 according to the species. As I pointed out in my previous 

 paper the dust material is no new discovery. The late 

 Dr. Fritz Miiller, whom little seems to have escaped, 

 described such hairs in the wing-folds of Hesperidae and 

 called them " chain-bristles," since they took the form 

 of long hairs constricted at regular intervals and liable 

 to break at each constriction. My friend Mr. A. H. Hamm 

 has lately called my attention to large masses of yellow 

 " fluff " occurring on the hind- wing of the male moth 

 Erebus macrops. I find this to consist mainly of " chain- 

 bristles " of an exceedingly beautiful form. 



The studies described in the present paper show how a 

 modest equipment of technique applied to suitable material 

 may disclose much that is interesting in the mere structure 

 of the organs in question, but of their physiology we know 

 little or nothing. If the simple brush of D. chrysippus can 

 perform its function efficiently what is the significance of 

 the five different structures found in the complicated brush 

 of A. egialeal The granules in the wing-cells of D. lotis 

 are not of the same chemical nature as the secretion 

 granules subsequently deposited in the brush. In what 

 does the change consist? Do some of these brushes 

 secrete a substance which combines with another stable 

 compound provided by the wing patch to form a volatile 

 oil? In A. niavius the wing-glands are neatly covered by 

 a layer of scales which seem precisely adapted for the 

 purpose of protection. Hence we might suppose that the 



