THE EVIDENCE OF THE CENTRAL NERVOUS SYSTEM 19 
results in the formation of a brain region more like that of the higher 
vertebrates than exists in Ammoccetes. 
In these cases the development is upward—the adult form is of a 
higher type than that of the larva. It is, however, possible for the 
reverse to occur, so that the individual development leads to degene- 
ration, not to a higher type. Instances are seen in the Tunicata, and 
in various parasitic arthropod forms, such as Lernea, etc. In these 
cases, the transformation from the larval to the adult form leads to 
degradation, and in this degradation the central nervous system is 
always involved. 
It is perhaps a truism to state that upward progress is necessarily 
accompanied by increased development of the central nervous system ; 
but it is necessary to lay special stress upon the importance of the 
central nervous system in all problems of evolution, because there is, 
in my opinion, a tendency at the present time to ignore this factor to 
too great an extent. 
The law of progress is this—The race is not to the swift, nor to 
the strong, but to the wise. 
This law carries with it the necessary corollary that the imme- 
diate ancestor of the vertebrate must have had a central nérvous 
system nearly approaching that of the lowest undegenerated verte- 
brate. Among all the animals living on the earth at the present 
time, the highest invertebrate group, the Arthropoda, possesses 
a central nervous system most closely resembling that of the 
vertebrate. 
The law, then, of the paramount importance of a steady develop- 
ment of the central nervous system for the upward progress of the 
animal kingdom, points directly to the arthropod as the most probable 
ancestor of the vertebrate. 
EVoLvurion or TISSUES. 
In the whole scheme of evolution we can recognize, not only an 
upward progress in the organization of the animal as a whole, but 
also a distinct advance in the structure of the tissues composing an 
individual, which accompanies that upward progress. Thus it is 
possible to speak of an evolution of the supporting tissues from the 
simplest form of connective tissue up to cartilage and thence to bone; 
of the contractile tissues, from the simplest contractile protoplasm 
