PALATABILITY 



119 



Planema aganice emits an acrid juice and A. echeria and Alaena amazoula are described as 

 having a nauseous taste and a strong smell. A. horta emits a bitter juice, but D. chrysippus 

 did not appear to have any taste at all, nor was any smell noticeable. In this latter respect 

 it is interesting to recall the evidence of Drs. Dixey and Longstaff, who both perceived a 

 strong odour about this butterfly. As pointed out by Professor Poulton in describing these 

 experiments, such tests are, and probably always will be, quite unsatisfactory and incon- 

 clusive. We cannot judge of the perceptions of insectivorous animals, or even assume that 

 there is any comparison to be drawn between their sensations and our own. The fact that 

 they refuse to eat certain insects whilst others are greedily devoured, is really all that con- 

 cerns us. It may be added that what we call taste, and especially the refinement of taste 

 expressed by the term flavour, is largely a matter of the olfactory sense. Now the sense 

 of smell is well known to be but poorly developed in human beings. The power of scent 

 in many animals is developed in a manner which we can but feebly comprehend, and hence 

 the sense of taste must be very greatly modified. Thus we see the baboons very clearly 

 distinguishing between M. agathina and B. mesentina with a delicacy of perception of which 

 we can have little real comprehension. We may compare in this connexion the words of 

 the late Sir Michael Foster,^ ' The sense of smell seems to play a far more important part 

 in the lives of the lower animals than it does in our life ; and what we now possess is probably 

 the mere remnant of a once powerful mechanism. We may perhaps connect with this, on 

 the one hand, the fact that, even in ourselves, the olfactory fibres have allotted to them what 

 is virtually a whole segment of the brain, namely, the olfactory lobe, and, on the other hand, 

 the fact that olfactory sensations seem to have an unusually direct path to the inner working 

 of the central nervous system. Mental associations cluster more strongly round sensations 

 of smell than round almost any other impressions we receive from without, and powerful 

 reflex effects are very frequent, many people fainting in consequence of the contact of a few 

 odorous particles with their olfactory cells.' These words are full of meaning for our 

 present subject. W^e can see how it may be probable that on the ultra-sensitive olfactory 

 organs of many animals ' flavours ' of which we are quite ignorant may have an effect 

 both powerful and lasting, and thus the possession by an insect of properties which produce 

 these sensations in their enemies may well turn the delicately adjusted balance of nature 

 in their favour. The experiments which have been described above can leave no doubt 

 in our minds that insects do in some cases actually possess such properties. It matters little 

 whether we call them taste or smell. If the existence of the objectionable character can be 

 associated in the mind of the captor with the appearance of the insect, as indeed the behaviour 

 of the baboons shows to be actually the case, then it requires very little argument to maintain 

 that the development, however evolved, of an imitative appearance in an edible species, 

 must of necessity confer on its possessor some share of whatever degree of immunity the 

 objectionable species may enjoy. 



It is greatly to be hoped that others whose work takes them to tropical lands, and 

 who are sufficiently interested in these subjects, will undertake further experiments on the 

 lines of Marshall's splendid work. The unexpected so frequently happens, when practical 

 tests are made, that even the amateur need not hesitate to add to our existing store of know- 

 ledge whatever results he may be able to obtain. Meanwhile it seems unnecessary to further 

 argue the broad question of the comparative inedibility of many insects. No unbiassed 

 reader could remain long in doubt after studying even the comparatively small amount of 

 work which has already been accomplished in this connexion. 



1 ' Textbook of Physiology,' Part iv, p. 1390. 



