liii 



Mr. J. W. Slater communicated the followiui,' paper; — 



" On certain Minute Characters of Insects, with reference to the 

 Theory of Evohition." 



" It has been contended, by no less eminent an authority than Dr. Lionel 

 Beale, that though animals belonging to nearly allied species, or even 

 genera, differ but little in the main features of their structure, yet on 

 minute examination of their tissues very striking and characteristic 

 distinctions are brought to light. He instances the difference between 

 the unstriped muscular tissue of the bladder in the common frog and in 

 the tree frog. 



"Again, as regards the chemical composition of the corresponding 

 solid matters, secretions, &c., of closely connected species, he contends 

 that very remarkable differences may be observed. Thus, the blistering 

 principle, known as cantharidine, is met with in all the species of Cantharis 

 that have been examined, and also in Melo'e, Mylahris, Ripiphorus, Zonitis, 

 and Cerocoma, whilst it has not been observed in the genus Sitaris, which 

 also belongs to the same group. On the other hand, a CoccineUa, and even 

 a spider [Ter/enaria medicinalis], have been successfully used for blistering. 



" To this I would object that the presence or absence of cantharadine in 

 insects seems in most cases to have been decided, not by actual chemical 

 analysis, but by medical experiment, and that when present in small 

 proportions, or when concealed among dense hard tissues, it may have been 

 easily overlooked. This supposition is the more reasonable as all the 

 species which have come into use as sources of cantharadine are very soft 

 in texture. 



" A curious fact has lately come to light in the order Hymenoptera. It 

 has been generally supposed that in the whole of the aculeate section of this 

 order the venomous liquid which tliey secrete and eject through their stings 

 was of an acid nature. That this is the case among the ants is well known. 

 But in the very next family, the Yespida;, an exception occurs. Professor 

 Church, having caused a wasp — species not named — to strike its sting into 

 a piece of turmeric paper, saw to his surprise that tlie poison was ratlier 

 alkaline than acid in its nature. 



"I purposed a re-examination of this question, but from the peculiar 

 character of the season I was only able to capture three common wasps and 

 not a single hornet. On causing the wasps to sting a piece of neutral-grey 

 litmus-paper it was quite evident that the poison was not acid. Neither 

 did it seem alkaline, as the spot produced was of a dull yellowish grey, and 

 soon became undistinguishable. On the other hand, bees of all the species 

 I was able to meet with secrete an acid poison, their sting producing in 

 every case a tiny red spot upon the litmus-paper. Wc find, then, this 

 peculiarity, that of all the stinging Hymenoptera, as far as we know, the 



