260 JOURNAL OF COMPARATIVE NEUROLOGY. 
phenomena are phenomena which are determined by ‘‘associa- 
tive memory,” and an animal possesses ‘‘associative memory” 
if it can be trained, if it can learn by experience. Such is the 
argument. BerTHE holdsa similar view when he says that an 
animal ‘‘that learns nothing, that always reacts in the same 
way upon the same stimulus, possesses no consciousness.” This 
doctrine may be called the theory uf pre-requisite development 
of the nervous system. In applying this criterion Professor 
Loes fails to find consciousness in such types as Infusoria, 
Coelenterates, and Worms, and doubts its existence in many 
higher forms. He is not sure as to Mollusks and Insects. He 
‘grants consciousness to Bees, Wasps, Spiders, certain Crabs 
and Cephalopods, but denies it to the common frog (Rana 
esculenta), though he finds it in the tree-frog. He is quite cer- 
tain of the presence of consciousness only in many of the 
higher vertebrates. His researches upon the plant and animal — 
tropisms leads him to think that wherever organic reactions are 
explicable by mechanical tropisms all reference to conscious- 
ness is excluded. ‘‘Associative memory’ comes in only when 
tropisms fail to explain the phenomena of adaptation. Hence 
consciousness appears abruptly in the course of a purely me- 
chanical evolution. 
That there is an important element of truth in the concep- 
tion that the ability to learn by experience is a mark of con- 
sciousness, we shall see later. The error in Professor LoEB’s 
view consists in identifying all consciousness with that particular 
type of highly organized consciousness which commonly goes 
by the name of ‘‘associative memory.’’ This might be a good 
criterion for testing the amount or degree of mammalian con- 
sciousness, but it is entirely too restricted a standard to apply 
to the whole animal kingdom, not to speak of the plant 
kingdom. 
Another theory of the criterion for the presence of con- 
sciousness stands midway between the extreme views just men- 
tioned, and is represented by such writers as SPENCER, MorGAN, 
Romanes, Eimer, and Carus. Moraan, for example, declines 
to say just where consciousness begins in the evolutionary 
