21 



flaps on account of the fine lines that run transversely across them, 

 and have been found present in all species examined. What then is 

 the meaning and function of these flaps ? Without a doubt they strengthen 

 the labium, but why the striae ? Fortunately in this case we need not 

 speculate on the structure of the organ from which they have come 

 down as rudimentary survivals ; for among the larvae collected during 

 the progress of this study, I have found two specimens possessing the 

 original organs of which these striae are the remnants. The striated flap 

 of one of these larvae (No. 7) is shewn in fig. i8a and 6, in which it 

 can be seen that the striae are prolonged into about twenty-four long bristles 

 or vibrissae projecting from the side of the head in a similar manner 

 to a cat's whiskers. In fig. 17 we have a highly magnified drawing of 

 the striated flap of C. piisio, in which it is evident that the striae are 

 equivalent to the roots of these vibrissae. In the second larva (No. 8) 

 the two forms are united in the same insect, that is to say the proximal 

 half of the flap is simply striated, while the distal half bears a number 

 of fully developed vibrissae. 



The larva No. 7 with a complete set of vibrissae is found in still Vibrissae. 

 and running water, in mud or rotting twigs, and does not seem to have 

 any definite instincts that can be in any way correlated with this 

 remarkable structure. Popular science has bestowed upon the cat's 

 whiskers the function of restraining the animal from attempting to pass 

 through too small apertures. MIVART in "The Cat" makes no mention 

 of this when speaking of the vibrissae, but it may be true nevertheless, 

 and if so we should expect the vibrissae of this curious Chironomus 

 larva to possess a similar function, but its habits as far as I have 

 observed them do not give any encouragement to this supposition. 



When we come to discuss the habits of C. piisio and its nearest 

 relatives, I shall endeavour to show that it is not necessary to suppose 

 that every fully developed organ is functional in all species which 

 possess it ; rather we must count ourselves fortunate if we find one or 

 two perfect examples. Of these latter I am persuaded that the bifurcat- 

 ing hairs in C. piisio are an illustration, while the vibrissae of Larva 

 No. 7 belong to the former ; that is to say they have lost their 



