RECENT TENDENCIES IN BIOLOGY 441 
changing the chemical environment, ctc. There is some 
internal mechanism in living matter that is influenced by 
changes in external conditions, and the study of the regulation 
cf 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), 
Marine animals are 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 larvee 
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 way in which animals will react toward light 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 important deductions 
regarding the nature of psychological processes. 
A line closely allied to experimentation is the application 
of statistics to biological processes, such as those of growth, 
