August, '14] REVIEWS 351 



thoroughness, as they represent the foundation of forest entomological practice. 

 Whosoever has learned to think correctly on these points will remain warned against 

 gross errors in practice." 



The chapter on insect-killing fungi was pi'epared by Dr. G. Lakon, while the "Rules 

 of Cultural Means of Prevention" come from Dr. W. Borgmann of Tharandt. 



A bibliography is given at the end of each chapter, listing the most important per- 

 tinent works. 



Special emphasis is laid on illustrations, of which the present volume contains 

 much more than double the number of those in the corresponding part of the old 

 edition. Only comparativelj' few of those in the old edition are here reproduced 

 (indicated by N at end of legend). The new figures are partly borrowed from other 

 works and partly original. 



The volume before us is divided into eight chapters with the followinj chapter 

 heads : 



Chapter I. Position of Insects in the System. 



Chapter II. External Appearance of Insects (Morphology). 



Chapter III. Internal Structure of Insects (Anatomy and Physiology). 



Chapter IV. Reproduction. 



Chapter V. In.sects as a Natural and Economic Power in General and especially 

 in reference to Forestry. 



Chapter "\T. Natural Limitation of Insect Increase. 



Chapter MI. Prevention and Control of Insect Calamities. 



Chapter VIII. General Survey of the System of Insects with a supplement: Guide 

 to the Establishment of a Forest Entomological Collection. 



The Chapter on Insects as a Natural and Economic Power covers the subject from 

 so many angles that it abounds in data of exceeding interest. After a brief discussion 

 of the average size of insects, the number of genera and species, the masses of indi- 

 viduals and their distribution in the various media, the author classifies the directions 

 in which the activity of insects is specially important as follows: 



1 . They hasten the disintegration of dead organisms. 



2. They destroy numerous living organisms and thus contribute to the mainte- 

 nance of the organic balance; 



3. Thej' constitute the necessary source of food of many other animals; . 



4. They bring about cross fertihzation of many plants; 



5. They assist in the distribution of the plant world, and 



6. They participate in soil building. 



Of these, 1, 3, and 4 were discussed by the original authors (Judeich & Nitsche), 

 2, 5, and 6 being new additions. Of these, the last two are of interest, primarily be- 

 cause based on most recent studies. 



In his discussion of the '^Degree of Dcsirudiveness of Forest Insects," the author 

 enumerates the following influencing factors: 



1. The biology of the given insect. 



2. The tree species. 



3. The age of the trees attacked. 



4. The health condition of the plants. 



5. The character of soil. 



6. The weather conditions. 



7. The season of the year in which the attack is made. 



8. The sylvicultiu"al conditions. 



9. The geographical position. 



Of these, the first one and the last two are not given, at least not in this connection, 

 in Judeich and Nitsche. This is what the author has to say under caption 8 in its 

 apphcation to the United States: 



