3i6 THE BIOLOGY OF THE FROG chap. 



region from which the nerves of the fore limbs arise that 

 the movements of these members are very naturally 

 affected. 



The Segmental Character of the Functions of the 

 Nervous System. — The functions of the central nervous 

 system of the frog bear out the segmental theory of the 

 action of the higher nerve centers which was first suggested 

 by Schrader and more fully elaborated by Loeb. The 

 nervous system of such forms as worms, crustaceans, and 

 insects consists of a series of pairs of gangUa connected by 

 a double nerve cord, there being typically one pair to each 

 segment of the body ; and as a rule each pair of ganglia 

 forms the center of the movements of the parts of the 

 segment in which it lies. Schrader at the close of his 

 paper on the functions of the brain of the frog gives expres- 

 sion to the segmental theory as follows : " The series of 

 experiments we have given teaches us that the central 

 nervous system of the frog can be divided into a series of 

 sections, each of which is capable of performing an independ- 

 ent function. It brings the central nervous system of the 

 frog into closer relation with the central nervous system of 

 the lower forms, which consists of a series, of distinct ganglia 

 that are connected by commissures. It speaks against the 

 absolute monarchy of a single central apparatus and against 

 the existence of different kinds of centers, and invites us to 

 seek for the centralization in the many-sided coupling of 

 relatively independent stations." 



Loeb has attempted to show that " the more complicated 

 instincts are for the most part nothing but a series of seg- 

 mental reflexes." " I am inclined," he says, " to recommend 

 using the word chain-reflexes whereby the performance of 

 one reflex acts at the same time as the stimulus for 

 setting free a second reflex. The taking of food may serve 



