RECENT TENDENCIES IN BIOLOGY 441 



changing the chemical environment, etc. There is some 

 internal mechanism in living matter that is inlluenced by 

 changes in external conditions, and the study of the regulation 

 of the internal processes that produce form and structure 

 have given rise to a variety of interesting problems. The 

 regeneration of lost parts and regeneration after intention- 

 ally-imposed injury has received much attention (Morgan). 

 Alarine animals arc especially amenable to manipulations of 

 this nature, as well as to alterations in their surroundings, 

 on account of the ease in altering the chemical environment 

 in which they live. The latter may be accomplished by 

 dissolving harmless chemical salts in the sea-water, and 

 observing the changes produced by the alterations of the 

 surrounding conditions. By this means Herbst and others 

 have produced very interesting results. 



In the field of artificial fertilization, free swimming larva? 

 have been raised from eggs artificially fertilized by changes 

 in osmotic pressure, and also by treating them with both 

 organic and inorganic acids; and these studies have greatly 

 altered opinion regarding the nature of fertilization, and of 

 certain other phenomena of development. 



Animal Behavior. — The study of animal behavior (Jen- 

 nings) is a very characteristic activity of the present, in which 

 certain psychological processes are investigated. These in- 

 vestigations have given rise to a distinct line of research par- 

 ticipated in by psychologists and biologists. The study of 

 the wav in which animals will react toward liiifht of different 

 colors, to variations in the intensity of light, to alterations in 

 temperature, and to various other forms of stimuli are yield- 

 ing very important results, that enable investigators to look 

 beneath the surface and to make im])ortant deductions 

 regarding the nature of psychological processes. 



A line closely allied to experimentation ih the application 

 of statistics to biological j^rocesses, such as those of growth, 



