624 



SCIENCE 



[N. S. Vol. XLII. No. 1087 



JoUa differs cliaraeteristically from the desert 

 form (sonoriensis) , but these differences relate al- 

 most wholly to pigmentation, that of the former 

 being of a deeper shade and more extensive in dis- 

 tribution. Hybridization between these two races 

 has proved easy, but I am not yet prepared to re- 

 port upon the results. 



The desert race has been transferred to the 

 humid atmosphere of Berkeley and reared success- 

 fully. Neither the parent animals, nor an Fi nor 

 an F, generation has shown, however, any per- 

 ceptible approach to the Berkeley type of colora- 

 tion. 



Some interesting modifications have resulted 

 from captivity. Mice of the subspecies gambeli 

 and sonoriensis, which have been reared from birth 

 in confinement, have been found to differ from 

 wild ones iu having a distinctly shorter tail, foot, 

 innominate bone and femur. No significant dif- 

 ference has been found in cranial capacity. 



These experiments are being continued at the 

 Scripps Institute, La JoUa. 

 Fossil Insects and Evolution: T. D. A. Cockerell, 



University of Colorado, Boulder, Colorado. 



The V. S. National Museum possesses a very 

 interesting series of English fossil insects, which 

 originally formed part of the Brodie collection, 

 but came into the possession of Laeoe, and finally 

 reached the museum with the Laeoe collection. 

 In the course of working over these specimens, oc- 

 casion was taken to review the fossil insects of the 

 British Islands, and incidentally to consider the 

 mesozoic insects of other countries. Since this 

 work was done, it has been ascertained that the 

 British Museum possesses very much larger collec- 

 tions from the same source, which it is hoped to 

 describe during the coming fall and winter. Meso- 

 zoic insects are of special interest because it was 

 during this epoch that most of the modern families 

 were established. The rise of the higher flowering 

 plants was necessarily contemporaneous with a 

 great development of insect life, and all the main 

 outlines of this development were certainly com- 

 pleted before the beginning of the Tertiary. Un- 

 fortunately our knowledge of Mesozoic insects js 

 extremely defective, but we know enough to reach 

 some interesting conclusions. The English Lias 

 contained great numbers of Coleoptera, and not 

 only were several of the modern families appar- 

 ently well established, but some of the species 

 showed a well-defined elytral pattern of longi- 

 tudinal dark stripes or bands, quite like the pat- 

 tern seen in various living beetles, and varying in 

 the same manner. Thus the outlines of elytral 



ornamentation, which might be imagined to be re- 

 cent and unimportant, are actually of enormous 

 antiquity, having been laid down before there were 

 any Lepidoptera, so far as we know, and even prior 

 to the appearance of Hymenoptera. 



Great advances have been made in recent years 

 in our knowledge of Tertiary insects, with the re- 

 sult of showing that on the whole progressive evo- 

 lution has been extremely slow, most of the new 

 species and even genera coming into existence by 

 a shuffling, as it were, of old characters. Wheel- 

 er 's researches on the ants of the Baltic amber 

 have shown that in the Oligoeene the Eormicoidea 

 were almost or quite as far advanced as they are 

 to-day. A comparison of the Miocene Bombycid 

 flies with those of to-day shows that at least in 

 certain features, the fossils are not rarely more 

 specialized than their modern representatives. 

 The Garnet Bay Oligoeene, a deposit in the Isle 

 of Wight, is full of beautifully preserved insects, 

 and when these have all been worked over we shall 

 know a great deal about the English insect-faunas 

 of that period. The work so far done confirms 

 the general opinion that evolution has been very 

 slow since that period, say within the last two 

 million years. Where genera are strikingly dif- 

 ferent from those now living, they have simply 

 become extinct. All this is of course very differ- 

 ent from the condition among the mammalia. We 

 are bound to conclude that the rate of evolution 

 is extremely different in different groups of ani- 

 mals. The insects are fairly comparable with the 

 Mollusca in this matter, but with this great dif- 

 ference, that the number of species of insects is 

 enormously greater, and the adaptations are much 

 more numerous and more diverse. The great sta- 

 bility of the main features of insect organization 

 is therefore more remarkable. On the other hand, 

 we find in the rocks many evidences of insect mi- 

 grations, or of the former existence of families 

 and genera where they are now extinct; so that we 

 are cautioned against assuming too much from the 

 present distribution of groups of insects. Insects 

 are in general mobile creatures, and, given vast 

 periods, may readily travel over the greater part 

 of the habitable world. They are, on the other 

 hand, commonly dependent on particular sets of 

 conditions, and thus they are likely to be locally 

 exterminated, the general result being a shifting 

 of insect populations in the course of time, obscur- 

 ing the original centers of distribution. 



H. V. Neal, 

 Secretary 

 {To be continued) 



