228 E. M. NELSON ON HAIRS UPON THE PROBOSCIS OF THE BLOW-FLY 



hairs there are others, which, in comparison, might be called 

 giant hairs, for at the base they are five times thicker than the 

 others are long. One measures "063 in length and -002 in 

 breadth, while a minute hair measures '00044 in length and 

 •000036 in breadth. These giant hairs, which are found both 

 upon the rostrum and upon the maxillary palpi, are ribbed 

 longitudinally, and a few of them have filamentous endings. 



In addition to these three kinds of hairs, there is a fourth 

 kind, ranged round the edge of the suctorial disc. These hairs 

 are about forty times as long as the minute hairs, and ten times 

 as broad. They are tubular, with a flat flange on either side. 

 They work on the same principle as the tongue itself, which is 

 admirably described by our past President, Mr. Lowne, in his 

 monograph on the Blow-fly, vol. i. p. 139. "The proboscis," 

 writes Mr. Lowne, " is an erectile organ. It is flaccid and folded 

 on itself when not in use, but is capable of being rendered rigid 

 by the injection of air into the extensive tracheal sacs which lie 

 in its cavities. When the proboscis is in use, it is projected from 

 the head capsule, and rendered stiff by the injection of air into 

 its trachea. Its varied movements are brought about by the 

 action of muscles; the flaccid proboscis is also folded and with- 

 drawn into the head capsule by means of retractor muscles. 1 ' 



The same supply of air which inflates the tongue also erects 

 these hairs. The object of this is twofold : first, it renders them 

 stiff enough to afford special protection to the delicate edge of the 

 suctorial disc, and, secondly, when the tongue is relaxed they 

 become flaccid and in no way interfere with the folding up of the 

 organ into the head capsule. One of these tubular hairs measured 

 •0187 in length and '00036 in breadth. All the measurements 

 are in fractions of an inch. 



My attention was first directed to these tubular hairs by 

 noticing that they were all blunt- ended, and in marked contrast 

 with the others, which had filamentous terminations ; from this 

 I was led to investigate their true character. In conclusion, 

 Mr. Merlin, who kindly undertook to examine these hairs, 

 states that his view entirely agrees with mine. 



Journ. Quekett Microscopical Club, Ser. 2, Vol. X., No. 62, April 1908. 



