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recovers its balance and resumes its dorsal 

 crawl, accompanied by a gentle swaying to 

 right and left. It also pitches to and fro. 

 The prow of the vessel, the larva's head, 

 rises and falls in measured oscillations. 

 The mandibles open and bite at space, appar- 

 ently trying to seize some support which is 

 lacking. 



Let us give it this support : not in the leaf- 

 mould, whose opacity would hide what I 

 want to see, but in a transparent medium. 

 I happen to have what I need, a glass tube of 

 some length, open at both ends and of a 

 gradually diminishing calibre. At the large 

 end the grub enters comfortably; at the 

 other end it finds a very tight fit. 



As long as the tube is more than wide 

 enough, the grub moves along on its back. 

 Then it enters a part of the tube whose cali- 

 bre is equal to that of its body. From this 

 moment the locomotion loses its abnormal 

 character. No matter what its position, 

 whether the belly is uppermost, undermost 

 or to one side, the grub advances. I see the 

 muscular waves of the dorsal pads moving 

 with a beautiful regularity, like the ripples 

 spreading over a calm sheet of water which 

 has been disturbed by the fall of a pebble. 



22 



