OCTOBEE 25, 1901.] 



SCIENCE. 



629 



This paper embraces some of the results 

 of the author's studies of the host plants 

 of nearly all the described, and some 100 

 undescribed, North American Scolytidse, 

 which in addition to the literature con- 

 taining references to the plants infested by 

 these beetles in all countries, enables him 

 to bring together for comparison a more 

 comprehensive list of the insects and plants, 

 than has ever before been possible. The 

 species of insects with observed or re- 

 corded host plants represent some 500 

 species, 52 genera, 20 sub-groups, 7 groups, 

 and 3 sub-families. All the host plants 

 are found to beloug to the Phanerogamse. 

 The Gymnospermse are represented by 1 

 order, 13 genera and 30 species. The 

 Angiospermge by 1 order and 1 species in 

 the Monocotyledons, and by 36 orders, 56 

 genera and 120 species in the Dicotyledons. 

 The paper is illustrated by a chart, showing 

 the relations of the primary and minor 

 divisions in the classification of the insects 

 with those of the plants. The genus of 

 plants infested by the species of any genus 

 or group of insects is shown in horizontal 

 spaces, while the genera of insects, con- 

 nected with any genera or group of plants, 

 are shown in vertical spaces, crossing the 

 horizontal ones. Thus the relations of 

 genera to genera, and group to group, are 

 presented in a most convenient manner for 

 study and comparison. In the relations 

 observed there seem to be some facts of 

 considerable taxonomic importance which, 

 if properly interpreted, and taken in con- 

 nection with structural characters of the 

 insects, will aid materially in determining 

 natural afiinities. When we came to con- 

 sider these facts, and apply the evidence 

 they furnish, towards the solving of some 

 taxonomic problems, some rather striking 

 results were obtained, which have guided 

 us to the discovery of some valuable specific, 

 generic and group characters in the insect, 

 heretofore entirely overlooked. Closely 



allied species and genera, which had been 

 relegated to far corners in different groups, 

 have been brought together, and order is 

 being restored where there was much con- 

 fusion. The evidence found in the fossils 

 of Eocene rocks, and in amber, indicates 

 that the Scolytidse reached a high stage of 

 development at the beginning of the Ter- 

 tiary, and that it is not at all improbable 

 that a maximum development was attained 

 during the Jurassic or Cretaceous. We 

 find the sequoia, and other survivors of 

 ancient groups of conifers ; the tulip, sassa- 

 fras, oaks, elms, beeches, poplars and other 

 survivors of primitive genera, and groups 

 of other plants, supporting what are be- 

 lieved to be the oldest surviving types of 

 groups and genera of Scolytidse. This, to- 

 gether with the evidence furnished by the 

 records of the host plants of existing 

 species, furnishes guides and suggestions to- 

 wards a clear conception of the probable 

 lines of evolution of present forms from 

 primitive generalized groups. They sug- 

 gest that the progenitors of the Scolytidse 

 may have found their way into the soft 

 bark and wood of conifer-like trees of the 

 first true forest in the Devonian ; or of the 

 thick soft bark of the great tree ferns, Sig- 

 illaria and Cicades, of the Carboniferous, 

 and that from these progenitors of the 

 Gymnosperms, Monocotyledons and Dicot- 

 yledons the descendants of the insects 

 have adapted themselves to the physiolog- 

 ical changes in the evolution of their hosts, 

 sharing with them the struggle for existence 

 through the changes in surface and climate, 

 from age to age, and from period to period, 

 to the present. 



8. 'Some Recent Observations on Cali- 

 cidse' : L. O. Howard, chief entomologist, 

 U. S. Department of Agriculture, Wash- 

 ington. 



An account of some new work on the bi- 

 ology of Aedes, Psorophora, Megarhinus and 

 Stegomyia. 



