PREFACE vii 



tion of the known facts of behavior in lower organisms, that might 

 be used, not only by the general reader, but also as a companion 

 in actual laboratory experimentation. This description, comprising 

 Parts I and II of the present work, on the Protozoa and lower Meta- 

 zoa, respectively, was made as far as possible independent of any 

 theoretical views held by the writer ; his ideal was indeed to present 

 an account that would include the facts required for a refutation of 

 any of his own general views, if such refutation is possible. These 

 designs have involved a fuller statement of details, with sometimes 

 their repetition under new experimental conditions, than would have 

 been necessary if the theoretical discussion had been made primary, 

 and only such facts adduced as would serve to illustrate the views 

 advanced. But the scientific advantages of the former method were 

 held to outweigh the literary advantages of the latter. 



As originally written, this descriptive portion of the work was 

 more extensive, including, besides the behavior of the Protozoa and 

 Ccelenterata, systematic accounts of behavior in Echinoderms, Ro- 

 tifera, and the lower worms, together with a general chapter on the 

 behavior of other invertebrates. The work was planned to serve as 

 a reference manual for the behavior of the groups treated. But the 

 exigencies of space compelled the substitution of a chapter on some 

 important features of behavior in other invertebrates for the system- 

 atic accounts of the three groups last mentioned. The accounts of 

 the Protozoa and of the Ccelenterata as representative of the lowest 

 Metazoa remain essentially as originally written. 



After this objective description was prepared, the need was felt 

 for an analysis of the facts, such as would bring out the general 

 relations involved. Part III is the result. Thus the conclusions set 

 forth in Part III are the result of a deliberate analysis of the facts 

 presented in a description which had been made before the conclu- 

 sions had been drawn. The selection of facts set forth in the de- 

 scriptive parts of the work has therefore been comparatively little 

 affected by the general theories held by the writer. The loss of 

 unity toward which this fact tends has perhaps its compensation in 

 the impartiality which it helps to give the descriptions. 



The writer is conscious of the necessarily provisional nature of 

 most general conclusions at the present stage of our knowledge, and 

 the analysis given in Part III is presented with this provisional 

 character fully in mind. The reader should approach it in a similar 

 attitude. 



Since the book is written primarily from a zoological standpoint, 

 it would be appropriate in some respects to entitle it " Behavior of 

 the Lower Animals." But the broader title seems on the whole best, 

 since the treatment of unicellular forms involves consideration of 



