Apeil 14, 1911] 



SCIENCE 



583 



too willful, while surplus people are almost 

 will-less. 



I do not use this argument to show that my 

 position is correct but to make clear what it 

 is on which the contrasted arguments rest. 

 The biologic sociologists are using bold de- 

 ductive arguments without a verification. 

 Their position has plausibility only by ignor- 

 ing observational evidence. Deductive medi- 

 cine with its neglect of diagnosis puts itself 

 in the same position. The one group affirms 

 that what is true of germ cells is true at ma- 

 turity while the other says what is true of 

 dogs holds for men. This is reasoning, not 

 observation or experiment. 



It is said of Agassiz that he took his stu- 

 dents out to a great boulder near Cambridge 

 and asked them what they saw on it. Some 

 saw nothing: others saw vague scratches. 

 Only he saw the ice-markings and proof that 

 the boulder was deposited by a glacier. By 

 the methods of to-day instead of these obser- 

 vatioHs we would have exact measurements of 

 the scratches : their depth and length would 

 be carefully ascertained, and finally the Car- 

 negie Institution would be asked to make a 

 grant for weighing the stone. In this way 

 note-books would be filled and a reputation 

 made, but who will say all this is worth as 

 much as what Agassiz saw with his unaided 

 eye? Logic has pitfalls for all of us: we es- 

 cape from our errors only by shrewd observa- 

 tions and multiple verifications. 



S. M. Patten 



University of Pennsylvania 



miastor larv^ 

 These remarkably interesting larvse, repro- 

 duced by pedogenesis, are available for labora- 

 tory work to a marked degree and must be 

 widely distributed as well as allied forms. 

 Very little is known concerning American 

 species, largely because their habitat is one 

 rarely explored by entomologists. They breed 

 mostly in decaying vegetable matter. We have 

 been very successful in finding them under 

 partially decayed chestnut bark of stumps, 

 fence rails and sleepers which have been cut 

 one or two years earlier. European species 



have been observed under the bark of a variety 

 of trees and even in sugar beet residue. 

 These dipterous maggots with diverging an- 

 tennse have a flattened, triangular head quite 

 different from the strongly convex, usually 

 fuscous head of the Bciara larvse occurring in 

 a similar environment. They have a length 

 of from one twentieth to one eighth of an 

 inch and may be found in colonies containing 

 a few large, white larvse with numerous 

 smaller, yellowish individuals, though the lat- 

 ter appear more common at the present time. 

 Early spring with its abundance of moist bark 

 appears to be the most favorable season for 

 finding the larvae. The writer would welcome 

 the cooperation of entomologists and others in 

 searching for these forms in diiferent parts of 

 the country. He will be pleased to determine 

 specimens found under various conditions, 

 make rearings therefrom if possible, and thus 

 add to our knowledge of the subfamily Hetero- 

 pezinse, a group which should be fairly abun- 

 dant in North America and one deserving 

 careful study. E. P. Felt 



Albany, N. Y. 



SCIENTIFIC BOOKS 

 Mineralogie de la France et des ses colonies; 

 description physique et chimiques des miner- 

 aux; etude des conditions geologiques de 

 leurs gisements. Par A. Lacroix. Paris, 

 Librairie Polytechnique, Baudry et Cie, 

 editeurs. 1893-1910. Pour volumes. 8vo. 

 Pp. XX + 723; 804; vi + 815; iii + 923. 

 This monumental work, which testifies at 

 once to the untiring industry of the writer 

 and to his thorough mastery of the material 

 he has collected, is destined to rank as one of 

 the most valuable contributions to the science 

 of descriptive mineralogy. It consists of 

 four large volumes, containing in all about 

 3,300 pages, and illustrated with more than a 

 thousand figures, a large number of which 

 are photographic reproductions of character- 

 istic specimens. The first volume was issued 

 in 1893, and at that time the author believed 

 that the work would be completed in two 

 years' time by the issue of a second volume; 



