March 9, 1900.] 



SCIENCE. 



389 



year, and in only a few instances have ob- 

 servations continued through a series of 

 years. We are all prone to generalize on 

 the facts in our hands, but it must be ac- 

 knowledged that the facts upon which we 

 can build theories of fresh water plankton 

 are very meager. There is need of a series 

 of examinations of typical lakes carried on 

 for a term of years, before we can build 

 with certainty. 



There remains the great problem, or com- 

 plex of problems, of the relation of the dif- 

 ferent elements of the plankton to each 

 other and to the fish. We see, frequently, 

 an apparent overproduction of one of the 

 elements. In shallow lakes — at least in 

 many of them — there is apparently a great 

 overproduction of vegetation. How is this 

 explained ? How is .the balance of life re- 

 stored ? What constitutes an ideal relation 

 between the vegetable and animal growth ? 

 When we plant a new species of fish in a 

 lake, we, of course, disturb the existing 

 balance of organisms, may we not, in some 

 cases, at least, work actual damage ? To 

 what extent is this balance between animals 

 and plants maintained in a lake that is not 

 interfered with by man ? 



These and similar questions, now with- 

 out answers, offer a field of almost un- 

 limited work, and work that is worthy 

 the best efforts of our students. For 

 while my address, in treating of the 

 present condition of the study of lakes, 

 has dealt largely with isolated facts, after 

 all it is not the facts which the student 

 pursues as his ultimate aim, but the general 

 laws underlying the facts. He is an unfor- 

 tunate man who sees the trees, but cannot 

 perceive the forest, who can see the stones 

 of which the cathedral is constructed, and 

 show how they were lifted to their places, 

 but cannot perceive the beauty of the struc- 

 ture as it stands in its exquisite proportions, 

 its massive masonry and wealth of sculp- 

 tured detail only serving to express the 



idea of beauty and harmony in the master 

 mind of the architect. 



C. DwiGHT Marsh. 

 EiPON College. 



SCIENTIFIC BOOKS. 

 The Cambridge Natural History. By David 

 Sharp, 'M.A. (Cantab.), M.B. (Edinb.), 

 F.R.S. Vol. VI. Insects (Part II.). Lon- 

 don and New York, Maomillan & Co. 1899. 

 8°. Pp. xii+626, and 293 cuts. 

 The completion of that portion of the Cam- 

 bridge Natural History which is devoted to in- 

 sects is an event of unusual importance to ento- 

 mologists ; for these two volumes constitute the 

 most useful work of its kind that has appeared 

 since the publication of Westwood'g Classifica- 

 tion of Insects. 



The most striking feature of this work is the 

 same as that which characterized Westwood's 

 Classification and has made it an indispensable 

 part of every entomological library ; that is, it 

 includes the results of a careful sifting of the 

 greater part of all entomological literature. In 

 a word, these two volumes of the Cambridge 

 Natural History constitute an encyclopEedia of 

 entomology, writtenby one whohas thoroughly 

 studied the more important contributions to all 

 departments of entomology, and who also con- 

 tributes much that is new. 



An admirable feature of the work is the fact 

 that it is well-balanced ; the morphology, the 

 taxonomy, and the CBCology of insects have each 

 received sufficiently full treatment. The stu- 

 dent of any phase of entomology is almost sure 

 to find someting on his subject here and to find 

 also references to the more important literature. 

 The author has placed entomologists under so 

 great obligations to him that one does not feel 

 like saying anything but praise of his work. I 

 cannot help feeling, however, that it would 

 have been better if in some respects he had been 

 less conservative. This is especially true of his 

 treatment of the larger divisions of the class 

 of Insecta ; his conclusions on this subject are 

 hardly an advance on what might have been 

 written a quarter of a century ago. In fact 

 this is the weakest part of his work. Thus, in 

 his discussion of Brauer's classification (Vol. 

 v., pp. 175-176), he has apparently failed to 



