404 



THE AMERICAN NATURALIST [Vol. LIII 



became active. This was true even if the gerrids previ- 

 ously had ])eeii inactive. They would start to jump and 

 walk in a very ao^ile, if ungainly, fashion, and made rapid 

 progress, especially if they were on a smooth and level 

 surface. It seemed tliat the transference from the water- 

 film to a solid surface— for all other conditions were as 

 before— was a sutlicient stimulus to cause iiiternal changes 

 in the insects, that set free energy in the form of loco- 

 motor activity. To induce this result there was but one 

 change in the conditions. In this connection I wish to 

 direct attention to a statement by Jennings (1906, p. 285) : 



Often, of coursi'. stimulation docs rouso an or<ranism to increased 



At this point, it may not be out of place to refer to cer- 

 tain observations which, possibly, may have a bearing on 

 the locomotor responses of the gerrids, after the drying 

 up of the pool of water. Abbott (1918, p. 234), in con- 

 nection with some responses of land isojKxls. Oi/iscus 

 aselhis Linn., Porcellio rathkei BrandK .iiid l'(>n<llio 

 scaher Latreille, to humidity and evapoiMt Ion innkcs the 

 following statement : 



to a dry atmosphere, including the first ^effect in desiccation exjieri- 



5. Behavior lu Dni Bed of B) ook. - \hou\ ten yards 

 farther downstream there was another iniich laraer i)ool. 

 Its dimensions were ;ii >iii'o\iiii;itc!>- y(l<. 2 yd^. ■ T) in. 

 I was interested to ()l.>ci'\c how iii;ui\. IimIimmI if of 

 the gerrids would re;i<-li it. tliii- ll.ic o\('i' the }MM-iod 

 of droiiu'lit. Of tile tw.Mily w;i t .T^t lid.M-. pi'<-oiit. oiu'ht 



