^ cxvi ) 



will explain tlio changes of conditions of life in time: and the 

 laws of variation, diversified in details as are the s]iecies 

 themselves, will ex])lain the rest." 



Mr. Bethiine Baker in his Address had occasion to refer 

 to the genera Ichthyunis and Psalidura, but he could hardly 

 have suspected how interesting an illustration of the modifi- 

 cation of parts those genera afford. Ichthy^nns is a genus in 

 which I had, myself, previously been very nuich interested 

 for another reason. It belongs to the family Telephoridae, 

 and several years ago I had discovered in nearly all the beetles 

 of this family a series of small apertures, distinct from the 

 spiracular openings, along the sides of the first eight dorsal 

 plates of the abdomen, a pair to each segment. In some 

 genera they lie well within the lateral margins; in others 

 they are placed close up to, or quite uj)on, the ])ostero-lateral 

 angles, excepting the first jiair, which always retain their 

 position inside the margin of the first tergite; and in a few 

 genera they are situated at the apex of very distinct lateral 

 processes which point outwards and slightly backwards. In 

 appearance these apertures are not unlike some forms of 

 spiracles; eacli has a ciicular chilinous rim bordering a small 

 pit lined with a pale membrane in which is a still smaller 

 opening fringed witli tine hairs, and which evidently is the 

 external opening of a gland. Segmentally arranged glandular 

 apertures of this kind are known in the larvae of some Coleo- 

 ptera, Lepidoptera, and other insects, and the secretion is 

 considered to be distasteful and ])rotective. Miss Olga Pa>aie, 

 with whom I was in correspondence when she was working 

 on the structure and life-history of one of our species of Tele- 

 phorus, has found the glands also in the larva of that genus, 

 and in the three thoracic as well as in the first eight abdominal 

 segments, and has given a descrij)tion of them in a paper since 

 ])ublished; but she has expressed a doubt as to whether they 

 are really functional, since the openings were very small and 

 no liquid secretion seemed to come from them. So far, how- 

 ever, as the imago is concerned, there can be no doiibt that 

 they are functional; for in handling some living specimens I 

 have myself seen drops of a clear liquid of pretty considerable 

 size issue from the pair of apertures on the eighth segment, 



