492 



IKE AMEIUCAX NATL HAL] ST [Vol. LIII 



captured from the surface-filni were put into a small 

 wooden box. This was taken to the place where the 

 other experiments were performed (Fig. 6). It was then 

 inverted and all the water-striders carefully shaken out 

 on to the ground one yard away fi-oin the water. It was 

 of course impossible to watch in detail evei'y gerrid, but 

 it w^as possible to observe how many of the hinnipterons 

 reached the water. The majority of them were back on 

 the surface-fdm within fifteen seconds after being placed 

 on the ground. All but two individuals had reached the 

 water within thirty-five seconds after the experiment 

 began. At the end of one minute of time all the gerrids 

 were on tlie surface of the pool. Sometimes a water- 

 strider was not successful in reaching the pool. These 

 statements are fairly typical of the results of many other 

 similar experiments. 



A series of exi)eriiHent^ of a similar character was 

 undertaken in which the gerrids were placed on the 

 ground three yards away from the pool. As in the ex- 

 periments one yard away from the water, the hemipterons 

 found the sui-face of the pool with reasonable promptness 

 and dirtH'tness. The greater number reached the water 

 within f()rt>' seconds from the time that they touched the 

 surface of the gr-ound. Tn the majority of these experi- 

 ments, all the water-striders were back on the surface of 

 the pool. -1 iiiiimtt's and T) seconds later. In each of two 

 diOViviit trial>, out of a total of six, there were two 

 gerrids that jumped awa\ from the pool and had not 

 reached the water at tlie time my o])servations were dis- 

 continued. 1 belie\^e that vision was the chief factor em- 

 plo>'ed in directing the gerrids to the water in the 

 exfXM-imonts when forty individuals wore used at each 

 trial. 



1 !iav.' n..t \«'t oI)-^ci-n(m1 tlir i(-nll^ of plarinu tho water- 

 stri<hM- the uTM,n„| in lai-e niiinhci- farliier auay 

 from t!ie pool than tlir.e yar<l^. Xor have I made any 

 tnal>. cither in the vieiriity ef ri-l>;,,ia oi' Syraeii^e. with 

 the iien-i<U fur a urealer .li.laiu-e from the uater than 

 four yards. 



