i68 THEORETICAL BIOLOGY 



victory, especially if the star-fish has recently fed well, and 

 so follows up the attack feebly. 



For another typical example we are indebted to the 

 remarkable investigations of J. Fabre. I am thinking of the 

 fight between the ichneumon-fly and the larva of the rose- 

 beetle. The ichneumon-fly seizes the larva with her jaws 

 on the dorsal side of the thorax, and bends her body round 

 the larva, while her sting carefully feels over the ventral 

 side until it comes to the place under which the ganglion-knot 

 lies. (We do not know what indication guides the sting.) 

 Then with her hollow lancet she makes one thrust, and smears 

 the ganglion-knot with a weak poison, which paralyses the 

 prey without killing it. The defensive movements of the larva 

 are completely unable to shake off the enemy for any length 

 of time. 



In this case the adjustment of the ichneumon-fly within 

 the prey-circle is very delicately worked out, and this is made 

 possible by the fact that the insect is concerned with one 

 particular kind of prey and no other. We may compare this 

 to the key of a safe, which is much more delicately wrought 

 than a skeleton-key, which has to open all manner of locks. 



The organisation of the larva of the rose-beetle is no match 

 for this delicate adjustment apparatus of the ichneumon-fly. 

 Its limits are too narrow. This is really not a battle, but 

 merely a conquest of the prey as soon as the predatory insect 

 discovers it. Naturally, the larva possesses other means 

 of defence, which favour its concealment from the enemy. 



Protective means of this kind are possessed by the eggs 

 of marine animals, which are cast defenceless into the sea. 

 They are either of glassy transparency and therefore difficult 

 to see, or else enveloped in jelly, or protected with armour, 

 or buried deep in the sand. 



The vast number of eggs that can be laid is to be reckoned 

 among the means at the disposal of the individual ; but as 



