V.—Researches upon the larch chermes (Cnaphalodes strobilobius, Kalt.), and their bearing upon the evolution of the Chermesinæ in general

The research which comprises the subject-matter of this paper was carried out at Oxford University in 1913 and 1914, and again over a period of three years from 1919 to 1921. During the former time observations were made mostly in the field, but the necessity of studying this Insect in isolated cultures obtained from a definite source soon became apparent, and not long after such cultures were started, in 1919, was it realised that they were of service in throwing light upon the evolution of the very peculiar sub-family of insects known as theChermesinæ . Insects falling into the OrderHomoptera comprise a number of well-marked families, of which theAphidæ are perhaps the most important. Of this large and varied family we need only mention two sub-families, thePhylloxerinæ andChermesinæ , which both have certain peculiarities in common with Aphids generally, in so far as they exhibit an alternation of a sexual generation with a sequence of asexual parthenogenetic generations. In the two sub-families the sexual individuals (male and female) are always wingless, and the parthenogenetic individuals may be winged or wingless, but that generation which produces the sexual forms is always winged. All the individuals are oviparous.Phylloxerinæ live upon Phanerogam plants, while theChermesinæ are confined entirely to Conifers. In addition to the alternation of generations referred to above, a second complication arises in the two sub-families, the members of which, throughout their life-cycles, show a marked tendency to produce offspring unlike the parent, but, in the very considerable literature which exists, it does not appear to have been remarked that in each case the parent shows a tendency to produce offspring similar in certain biological and structural characters to the grandparent.