Mat 10, 1907] 



SCIENCE 



729 



A Study in Variation, Geographical Dis- 

 triiution arid Mutation in Snails of the 

 Genus Partula from Tahiti: H. E. 

 Crampton, Columbia University. 

 In presenting the more important results 

 of a recent study in the field of terrestrial 

 pulmonates of the island of Tahiti, belong- 

 ing to the genus Partula, it was shown that 

 different valleys contain forms that on ac- 

 count of their more or less complete isola- 

 tion have come to differ in correlation with 

 their geographical proximity or remoteness. 

 The vital conditions that limit the snails 

 of this island to their particular stations 

 are dryness peripherally, where the valleys 

 debouch upon the coastal alluvial plain, 

 and lower temperature centrally. Only 

 rarely may stragglers pass from one region 

 to another. 



Evidence was adduced showing that 

 'mutations' have arisen at various recent 

 times, the observations of Garrett and 

 Mayer, taken in connection with the results 

 of the writer, making it certain that at 

 least three forms have thus originated, at 

 dates that may be determined with sub- 

 stantial accuracy. It was furthermore 

 shown, in corroboration of Mayer's conten- 

 tion, that the environmental conditions can 

 not be regarded as the factors that have 

 produced the several specific and varietal 

 differentia exhibited by the Tahitian 

 snails. 



On a Case of Reversion induced iy Cross- 

 Breeding a/nd its Fixation: W. E. 

 Castle, Harvard University. 

 This paper has been published in Sci- 

 ence of January 25. 



Reversion: C. B. Davenport, Cold Spring 

 Harbor, Long Island. 



Observations on the Habits of Salt Marsh 

 Mosquitoes: John B. Smith, New Bruns- 

 wick, N. J. 

 During the summer of 1906 a close watch 



was maintained on the development of 



mosquitoes on the salt marsh area near 

 Elizabeth, New Jersey. In all ten distinct 

 broods developed, the first observed April 

 19 and coming to maturity May 2; the 

 tenth observed October 12 and coming to 

 maturity soon after. Larvae were found 

 however until November 30 after even 

 heavy frosts. Broods I., II. and III. were 

 mostly Cidex cantator; in brood IV., C. 

 cantator and G. sollicitans were almost 

 equal ; brood V. had 80 per cent, cantator, 

 and after that C. sollicitans was in the 

 majority in all cases. The latest larvae, 

 however, were cantator. There was a 

 great difference in the habits of the various 

 broods: I., II., IV. and VI. were migrants 

 and left the marshes in great numbers; 

 the others remained on the marshes or did 

 not get very far inland. There seemed to 

 be a relation between numbers and migra- 

 tions, the heavy broods migrating most and 

 farthest. 



An Undescribed Species of Noctuid Moth 

 from New York City: Henry Bird, Rye, 

 New York. Illustrated by box speci- 

 mens showing larvEe and habits. 



New Evidence from Primitive Sharks on 

 the Origin of the Limbs of Vertebrates: 

 Raymond C. Osbuen, Columbia Uni- 

 versity. 



Embryological studies on Eeterodontus 

 japonicus Dumeril, a cestraciont, and on 

 Chlamydoselachus anguineus Garman, a 

 notidanid shark, show that there is a deep- 

 seated, primary similarity between the 

 paired and unpaired fins embracing all the 

 structures of the fins— skeleton, muscles, 

 nerves, blood supply and ceratotrichia. 

 The arguments recently advanced by the 

 gill-arch theorists for the branchial origin 

 of the paired limbs (viz., abortive muscle- 

 buds, fusion of muscle-buds, collector 

 nerves, discrepancy between muscle and fin 

 rays, and fin-migration) are all disposed 

 of by showing that these conditions may 



