TRANSACTIONS OF SECTION D. 765 



or the secretion of formic acid greatly affected the lizards. The terrifying hut 

 quite harmless larvte of Chmrocamim elpenor, which is known to frighten all but 

 the boldest of birds, as Weismann has shown, was offered to a laj'ge lizard. The 

 latter examined the larva most cautiously and many times before touching it ; 

 then it bit the larva gently, and retired to watch the effect, repeating this process 

 several times. Finally, finding tliat nothing happened, it seized the larva and soon 

 swallowed it. The etlect produced by this serpent-like larva was not due to its 

 size, for the equally large larvse of Smerinthus occllatus were seized at once. 

 The imagines of Sesia bembecifnyinis and 'S'. apiformis — resembling hornets — were- 

 offered to a lizard. On the first occasion the moth was approached with the 

 greatest caution, examined carefully, and seized by the head and thorax, just as 

 though it possessed a sting. At the same time the lizard was evidently suspicious 

 of the apparent wasp or hornet at first sight. AVhen a tew days later a second 

 moth was offered to the same lizard it was immediately seized without any 

 caution or hesitation. The lizard had learnt its lesson. Instances of this kind 

 support the belief that insect-eating animals have no instinctive knowledge of the 

 palatable or unpalatable or dangerous character of their prey, but that they learn 

 by experience. Thus the chameleon was offered a bee, which was caught at once 

 with the tongue ; as the organ was withdrawn the chameleon was stung, and 

 shook the bee off"; after this it would never touch a bee again. Similarly with 

 many conspicuous nauseous insects ; they were generally caught once, but rarely 

 a second time. Now if such instinctive knowledge existed, the chameleon, above 

 all, might be expected to possess it, because of the manner in which it catches 

 insects. Shooting its prey from a considerable distance, it can rarely gain any 

 knowledge of a new insect without, so to speak, committing itself; whereas other 

 lizards can make use of the tactile sense in their tongues, while their sense of smell 

 must be more efficient because of their greater proximity before capture. It 

 appears, however, that the chameleon brought among tlie insects of a new country- 

 relies solely upon a good memory and powerful sight : and these are so efficient 

 that a single instance of each species of insect is sufficient for a thorough 

 education. If, however, tlie chameleon depends upon instinctive knowledge for the 

 avoidance of nauseous insects in the countries where it is indigenous, we should not 

 expect that its education in strange countries would be so rapid and complete as it 

 has proved to be. 



All the species of the genus Zyrjana hitherto tested are nauseous, and all are 

 conspicuous and strikingly similar, so that it is probable that we have here an 

 instance of divergence checked by the advantages which follow from simplifying 

 the education of enemies by setting them one pattern to learn instead of several. 

 Instances of this are well known in other countries, but this is the first example ia 

 our own fauna. 



Among all the experiments previously recorded there occun-ed no instance of an 

 unpalatable imago which had been palatable in eariier stages. I have paid especial 

 attention to working through many histories in this way, and as a result I have 

 found one such instance. The larva of Arcfia caja is unpalatable because of the 

 presence of hairs, but apparently not otherwise ; the pupa is palatable, while the 

 imago is highly conspicuous and extremely nauseous. 



5. The Secretion of Fure Aqueous Formic Acid hy Lepidopterous Larvce for 

 the purpose of defence. By E. B. Poulton. 



It has been long known that the larvas of the genus Ceri/ra (Diirmiura) have 

 the power of ejecting a colourless fluid from the mouth of a gland which opens on 

 the prothoracic segment. The latter segment is dilated when the larva is irritated, 

 so that the fluid is thrown in a forward direction, and for a distance of several 

 inches. When the larva is touched the head and anterior part are immediately- 

 turned towards the source of irritation, and the fluid is thrown in this direction. 

 In 1885 I found that the secretion was strongly acid to test paper, and that it 

 caused very strong effervescence when placed upon sodium bicarbonate : while a. 



