34 



the presence of a distinguished visitor, Dr. Barker, of Dublin, said he thought 

 it might be well to read the letter by Dr. Hollis, in the last number of 

 " Nature," bearing upon the subject of Professor Pfliiger's observations. (The 

 President then read the letter referred to.) fie confessed that he was not con- 

 vinced even before Mr. Lowne had spoken. Certainly he did not regard the 

 presence of tracheae as conclusive, for he had a specimen of the eye of a drone 

 fly which was full of tracheae, and no one would doubt that it was an eye 

 because of these tracheal tubes ! He thought that, on the whole, the reasoning 

 was quite inconclusive. 



Mr. T. C. White said that he had dissected many of these insects, and had 

 found the tubes in every case [collapsed. He had, in some cases, sealed up the 

 mouths of the insects before killing them, and still had found them collapsed. 

 He had also kept the insects for two days in a carmine solution placed under 

 the air pump, but with the same result. 



Mr. Loy said he had had some practice in dissecting these insects, and, from 

 what had come under his own observations, he certainly agreed with Mr. 

 Lowne. He believed that these organs were secretory vessels, and he had 

 never found the slightest evidence of air in them ; and although they were 

 found closed, it was by no means impossible that there might have been some- 

 thing in them. He felt quite sure that they were not tracheal tubes, because 

 these were at all times easily recognised by their silvery appearance. His own 

 idea was that they were merely reservoirs in which the saliva was stored until 

 pumped by the tube to the stomach. He differed from Mr. Tatem in regarding 

 them as assistants to flight. In a large number of insects examined he had 

 never found any evidence of tracheal or air sacs forming part of their salivary 

 glands. 



Mr. T. 0. White said that in the cockroach there were two enormous tracheal 

 ducts, but there was no connection whatever between the tracheal system and 

 these salivary sacs. 



Mr. Loy said that this could be seen in the specimens. 



Mr. Lowne said Mr. Loy had observed that there was a difference in the colour 

 of the two sets of glands, and this would seem to confirm the idea that there 

 were different kinds of saliva. In Catypsa, and also in the silkworm, it was 

 quite evident there were two kinds. 



The President inquired if any peculiarity had been observed in the saliva of 

 insects which inflicted poisonous bites ? 



Mr. Lowne referred the question to Mr. Loy. 



Mr. Loy said that all those fluids were very irritating, but he was not aware 

 of their precise nature. He had noticed that in the case of the caterpillar of 

 the Dicranura, a small globule was thrown out immediately the creature was 

 irritated, and that it came from an orifice situated just below the mouth. In 

 action he thought that in the process of feeding the caterpillar pressed this 

 gland upon ithe edge of the leaf, and lubricated it as it proceeded. He had 

 killed them immediately after the discharge of the fluid, and had then found 

 the bag empty. 



The President asked if there was any truth in the idea that the saliva had the 

 effect of thinning the blood, so as to enable the insect to draw it in more 

 easily ? 



Mr. Loy could not speak positively upon this point. 



Mr. Hailes could not see in what way these glands could assist in flight, even 

 if they were filled with air— seeing that the insect flew in air. The analogy to 

 the fish would hardly hold good, because if the fish filled its air bladder with 

 water, it would make no difference whatever in its specific gravity. 



