June 7, 1907] 



SCIENCE 



901 



Much confusion, both to the students of dis- 

 tribution and of pedigree cultures, has resulted 

 from this lack of formulated criteria. Some 

 may question the possibility of such criteria. 



After such detailed studies, in which special 

 emphasis has been placed upon geographic 

 origin, one naturally expects certain criteria, 

 perhaps more or less peculiar to the ecological 

 relations of crawfishes, to be formulated, but 

 such are not stated. 



Two important papers should perhaps be 

 mentioned in this connection, as they are not 

 listed in the bibliography: Harris, 'An Eco- 

 logical Catalogue of the Crayfishes belonging 

 to Genus Cambarus' (Eans. Univ. Sci. Bull., 

 Vol. II., pp. 51-187, 1903), and Steele, ' The 

 Crayfish of Missouri' (Univ. of Cincinanti 

 Bull, No. X., pp. 1-54, 1902). 



A certain amount of statistical data could 

 have been used to advantage. As this method 

 of measuring variation, used with judgment 

 and moderation upon critical phases and at 

 critical localities, will aid such investigations. 

 For example, if representative lots of hartoni 

 from the northwestern, central and eastern 

 parts of the state had been measured, the rate 

 of dwarfing could have been determined. A 

 similar comparison between the western and 

 eastern variation of diogenes would be of 

 value. Such variations as these are very com- 

 mon and signify to some that very frequently 

 the species is too large a unit for the study of 

 geographic distribution, that local variations 

 or races are of great importance and that in 

 further investigation the forms peculiar to 

 definite habitats should receive recognition 

 and detailed investigation. 



In conclusion it should be said that such 

 excellent work, perhaps the most important 

 general zoological work yet published by the 

 Carnegie Museum, should be continued, as the 

 subject has reached such a degree of develop- 

 ment that to stop now would be unfortunate, 

 to say the least. The region to the south and 

 west should now be considered, not only be- 

 cause of its proximity to Pittsburg, but pri- 

 marily because it is apparently in that direc- 

 tion that a most wonderful evolution of craw- 

 fishes has taken place, or is taking place. 

 Then with the modification of original condi- 



tions through the ' improvement ' of streams 

 for navigation, water power and supplies, the 

 construction of canals, contamination by in- 

 dustrial refuse and sewage, we have additional 

 urgent reasons for an early continuation of 

 such investigations so that ' vanishing data ' 

 will be preserved for future generations. The 

 Carnegie Museum is not a provincial institu- 

 tion, and does not necessarily limit its activi- 

 ties to the state of Pennsylvania, and it is 

 hoped that this work will be continued, as the 

 present study has clearly shown that the most 

 important part of the problem still awaits de- 

 tailed investigation. 



Chas. C. Adams 

 Univeesitt of Cinoinnati, 

 Cincinnati, Ohio 



SCIENTIFIC JOURNALS AND ARTICLES 

 The Journal of Comparative Neurology and 

 Psychology for March contains a report of 

 the convocation week meetings held in New 

 York city during the winter, including ab- 

 stracts of most of the papers read before the 

 various societies in the fields of neurology and 

 animal behavior. The leading article is a 

 memoir on 'Light Reactions of Volvox,' by 

 S. 0. Mast. The light reactions were studied 

 under rigidly controlled conditions in the 

 ' light grader ' devised by the author. Among 

 other results, it was found that the direction 

 of motion in Volvox is regulated by the rela- 

 tive light intensity on opposite sides of the 

 colony regardless of the ray direction. Ori- 

 entation is not the result of ' trial and error ' 

 reactions, as in Stentor, Euglena and other 

 forms. Volvox colonies make no errors in 

 this process. There is no evidence of motor 

 reaction in a Volvox colony, taken as a whole. 

 Orientation is, however, brought about by 

 motor reactions in the individuals which con- 

 stitute the colony. Weber's law holds ap- 

 proximately for the light reactions of Volvox. 



The American Naturalist for April has for 

 its leading article a discussion of ' The Geo- 

 graphic Distribution of Closely Related Spe- 

 cies,' by Robert G. Leavitt. The question is 

 considered from a botanical standpoint and 

 the author's conservatively stated conclusions 



