46 LECTURES ON BIOLOGY 



obvious. Many beetles and spiders collapse on the floor as soon 

 as they are touched, draw in the limbs close to the body and 

 4 pretend to be dead.' In this state they frequently remain 

 a considerable time. As a resting object is notoriously more 

 difficult to discern than a moving one, especially if its colour 

 does not greatly differ from that of its surroundings, they 

 frequently escape by this artifice from the persecutions of their 

 enemies. As, further, many animals seize only living and moving 

 prey, but pass by motionless objects, this ' pretence to be dead ' 

 is of considerable advantage to those animals which practise it. 



An interesting observation is reported by Belt. Several 

 locusts had met a detachment of the murderous Driver-ants. 

 Some of the locusts forthwith became paralyzed with fright, and 

 being rigid and motionless, escaped death ; others sought salva- 

 tion in flight, but were quickly caught, overpowered and devoured. 



It is necessary to say a word about the attitude of many 

 organisms to chemical influences. Here we see that conditions 

 which are fatal to one organism have often not the least dele- 

 terious effect upon others. In zoological practice pure alcohol 

 and osmic acid are two of the strongest and most frequently 

 used means of preserving. With the majority of the smaller 

 animals an immersion lasting only a few T seconds, or, at the 

 most, minutes, is sufficient to kill them and harden the tissues. 

 But if we place the aquatic larva of Corethra plumicornis, a 

 species of gnat, into either of these liquids it swims placidly 

 about, just as if it were in its proper element. After a con- 

 siderable time it begins to show signs of unrest, but frequently it 

 is only after several days that this delicate little animal succumbs 

 to the effects of the poison. 



Still more wonderful appears the life of a little worm 

 (Anguillula aceti) which lives in vinegar. Where no other life 

 can exist this tiny worm, which does not exceed 2 mm. in length, 

 grows and multiplies, feeling as comfortable as a fish in water. 

 If one holds up a bottle of vinegar to the light one may frequently 

 see many of these ' thin threads ' swimming gaily about. 



Nature places before us riddle after riddle. Inexhaustible are 

 her ways and means of providing for her creatures suitable con- 

 ditions of existence, and even to unlock for them such regions 

 as according to our idea of living organisms would seem to 



