366 STUDIES IN GENERAL PHYSIOLOGY 
which has been cultivated in the North it is to be attributed 
to a difference in the constitution of the tissues of the 
two plants, possibly to a difference in the amount of water 
contained in the two tissues. The periodic depth migra- 
tion of the Medusa are, as I believe, brought about through 
a periodic change resulting from internal causes in the 
amount of water contained in the animal, which, in the 
temperate zones, corresponds in its period with the change 
of day and night. (I suspect that the light brings about 
a change in the amount of water contained in the animal 
in one sense, while darkness brings it about in the oppo- 
site sense.) When the Medusa is then transferred to the 
North there is no occasion for a change in the period. In 
associative memory, on the other hand, we have to deal, it 
seems to me, with a definite mechanical arrangement which, 
from experiment and pathological experience, has to be 
sought in the brain and which is present only in certain 
animals, while it is missing in others. Correspondingly 
consciousness is present also only in certain animals, and in 
these only after a certain stage in embryonal development 
has been reached. To claim, as does one English author, 
that a “‘subconsciousness”’ exists in the egg, I consider just 
as wrong as though one would say that a subphonograph 
exists in a drop of water. The Darwinian habit of seeing 
transitions everywhere becomes erroneous when it attempts 
to take into consideration machines which yield qualified 
energy. And we have to do with such machines in the case 
of associative memory, as well as in many other physiological 
apparatus.’ 
4. If, therefore, a decided difference exists between 
many vertebrates and the worms (and other lower animals) 
so far as associated memory and consciousness are concerned, 
1In many respects my views coincide with those expressed by DrrEsca in his 
excellent booklet Die Brologie als selbststéndige Wissenschaft. 
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