264 SELIG HECHT 
fore called ‘the reflex’ (Loeb, ’02). Jordan (’07) has more appro- 
priately called it the protective reflex (Schutzreflex). 
The reactions which are comprised in this direct group show 
individual variations depending upon the intensity of the stimulus 
which sets them off. They can, however, be very definitely 
separated from one another when the animal is observed with 
any degree of care, or when graphic methods are employed. (See 
for example, figure 8 of the first paper of this series: Hecht, 717.) 
All these reactions are to be kept apart from those which are 
in the group of crossed responses. The stimuli which result in 
the reactions of this second type are all localized on the interior 
surfaces of the siphons, of the atrial cavity, and of the branchial 
sac. They include changes in the environment not only of a 
mechanical nature, but of a thermal, photic, and chemical kind 
as well. 
Although they may be produced by the same kind of stimulus 
varying in intensity, the three reactions included in this group 
are, nevertheless, the result of different combinations of effectors. 
As in the case of the direct reflexes, they must, therefore, be 
sharply distinguished one from another. To make this clearer, 
I may refer to the behavior of a human being suddenly exposed to 
a bright light. The person will reflexly close his eyes. If, how- 
ever, the light be made excessively bright, he will not only close 
his eyes but also place his hand over them. The nature of the 
stimulus is the same, but the greater intensity of the stimulus 
brings forward a new activity superimposed upon the simple eye 
closure. The same is true of the following reactions of Ascidia. 
1) An exceedingly delicate stimulus on the inside of one siphon 
results in a closure of the other siphon. The stimulated siphon 
remains wide open, while the sphincter of the other siphon is 
called into play. This kind of response can be secured only 
under very carefully controlled conditions. The animal must 
not be jarred and the stimulus must be a delicate one. It is 
best to use large animals because they are not as sensitive as the 
smaller ones. 
2) An increase in the intensity of the stimulus produces a re- 
action which does more than merely stop the water current; in 
