viii Journal of Comparative Neurology. 



ence between an animal and a plant in this respect is mainly in the 

 greater rapidity with which an animal reacts rather than in any essential 

 difference between its reactions and those of plants. The nervous sys- 

 tem, then, in its simpler operations is a means for the rapid transmission 

 of nervous impulses from sense organs to organs of reaction, muscles, 

 etc. The question of coordin ated reflexes is next considered and it is 

 declared that coordination is mainly apparent and is brought about in 

 any group of elements not by a coordinating center, but by that ele- 

 ment which temporarily possesses the most rapid rate of discharge and 

 which impresses that rate for the time being on the associated elements. 

 If the simple and coordinated reflexes and even those aggregates of in- 

 herited reflexes that we call instincts are at bottom only delicately 

 adjusted transmissions of nervous impulses and therefore in no sense a 

 test of intellect, what criterion can be used for the psychic qualities of 

 animals ? To this Professor Loeb answers, associative memory. An 

 animal to have the most rudimentary form of psychic life must have 

 the power of associating its past nervous experience with its present. 

 It must be able to learn. Having this power the animal may develop 

 consciousness ; without it, such a step is absolutely impossible. 



Following the introduction is a series of chapters dealing in a sug- 

 gestive way with the nervous activities of a graded set of animals. 

 These include a consideration of the medusae, ascidians, actinians, 

 echinoderms, worms, arthropods, molluscs and vertebrates, and outline 

 the development of nervous activities in the animal series. 



The concluding chapters deal with general problems of the central 

 nervous system, and, while these are more or less associated with the 

 higher animals, proper treatment is accorded them, as Professor Loeb 

 all along points out, only from the comparative standpoint. The sub- 

 ject matter of this part of the work includes such as the physiological 

 aspect of the segmentation of the vertebrate central nervous organs, 

 animal instincts, the central nervous system and inheritance, criteria for 

 the determination of consciousness in lower animals, the brain and 

 consciousness, and the theory of the localizations of nervous centers. 



The observations recorded in this work are in the mam matters with 

 which Professor Loeb is acquainted at first hand and the vigor and ac- 

 curacy of the text is doubtless owing in large measure to this fact. Here 

 and there are questionable statements such as are to be expected in the 

 first edition of a book covering so broad a field. Thus, in the account 

 of the reactions of planarians, the fact that their movements are accom- 

 plished in part by muscles that are probably controlled by a nervous 

 mechanism and in part by cilia probably independent of nervous in- 



