January 3, 1913] 



SCIENCE 



23 



•of the latter groups, illustrated by the scheme, 



CH, . CHNH, . COOH ^ CH3 . CO • COOH ?± 

 CH3 . CHOH . COOH, 



furnishes a text for the discussion of some of 

 the manifold metabolic performances that 

 have only lately found a place in physiological 

 speculations. The oxidation and reduction of 

 amino-acids by microorganisms, with reference 

 to the splendid newer werk of F. Ehrlich and 

 of Neuberg in this field, is presented in novel, 

 though brief form. In his treatment of the 

 behavior of the carbohydrates Dakin cham- 

 pions the view that lactic acid must be re- 

 garded as one of the most important sub- 

 stances concerned with their intermediate 

 metabolism. There are further chapters on 

 the purines, hydrocarbons, phenols, etc.; and 

 in conformity with the plan of the series of 

 monographs on biochemistry to which this 

 book belongs there is a well-arranged bibliog- 

 raphy appended. 



The frankness with which open questions 

 are presented, as illustrated in the debated 

 respective roles of ^-ketonic and j8-hydroxy 

 acids, is wholesome and marks the unbiased 

 attitude of the book's author, even where his 

 own researches are involved. The reader is 

 impressed with the great advances which have 

 lately been made in the new field covered by 

 thi^ monograph; and whether his interests are 

 primarily those of the physiologist or the 

 chemist, he will be stimulated by the wealth 

 of suggestions — all presented there in a read- 

 able form. 



Lafayette B. Mendel 



Sheffield Scientific School, 

 Yale Univeksitt 



The North American Dragon Flies of the 

 Genus Mshna. By E. M. Walker. Uni- 

 versity of Toronto Studies. 1912. 

 It occasionally happens that some familiar 

 group of animals is investigated by one who is 

 sufficiently skilled and independent to detect 

 •characters which have escaped all previous ob- 

 servers. I recall the time, now a quarter of a 

 century ago, when certain common land mol- 



luscs were added to the British list. One of 

 these was almost literally in every one's gar- 

 den, but until its distinctive characters were 

 pointed out, nobody could see it. To-day the 

 merest beginner can recognize it at once. We 

 are forced to conclude that even excellent 

 manuals are not without their disadvantages, 

 when they are blindly followed by naturalists, 

 who will not even look for things unmentioned 

 by them. The same sort of thing has been 

 very evident in botany, and we have in Mr. 

 Walker's work a remarkable exposure of blind- 

 ness in the field of entomology. Mr. Walker, 

 during the summer of 1906, was at Lake Sim- 

 coe, Ontario, where he interested himself in 

 the common large dragon flies of the genus 

 JEshna. Most people would have viewed them 

 with languid interest as being among the 

 "familiar objects of the country side," com- 

 pletely exploited by entomologists long ago. 

 Not so Mr. Walker, who with critical eye 

 presently discerned that there were more spe- 

 cies than the books called for. His curiosity 

 thus stimulated, he pursued the subject 

 further, and was eventually able to establish 

 the existence of sixteen perfectly valid species 

 in temperate North America, five of them de- 

 scribed as new by himself. W bile doing this 

 he has monographed the genus as represented 

 in this country, and now publishes a most ex- 

 haustive treatment, discussing the biology, 

 early stages, geographical distribution and 

 other matters. The work is also fully illus- 

 trated, with 28 plates and some good text fig- 

 ures. Only one thing seems lacKing: i find 

 no mention of Scudder's /Eshna soLida, which 

 is represented by such beautifully preserved 

 wings in the Miocene shales at Florissant. 



The interesting fact is brought out that in 

 addition to " structural " characters, each spe- 

 cies has its own color-pattern, which may at 

 once be recognized when known. It is also 

 found that the immature forms, the nymphs, 

 have characters of their own, which are duly 

 set forth in a key. it is thought probable or 

 possible that the genua Jishna is of polyphy- 

 letic origin, the californica group especially 

 having perhaps a different origin from the 



