V CADDIS-WORMS 247 



are kept moist by a liquid which flows from them. 

 Is it possible that these prominences help in respira- 

 tion ? " 



Mr. T. H. Taylor has, at my request, examined 

 these retractile processes with care. His inquiry is 

 still incomplete, but has already yielded results of 

 interest. The processes are believed to be best 

 developed in the Phryganeidae, but as yet little has 

 been done to study the various families comparatively. 

 The processes in question are absent in those Caddis- 

 worms which construct no movable sheaths. The 

 median tubercle may be the most completely retractile 

 of the three ; ^ the lateral ones are armed at their 

 extremities with peculiar scales, notched at the 

 extremities. 



The fact that these processes are absent in the 

 Caddis-worms without sheaths suggested that they 

 might possibly be used to regulate a flow of water 

 through the sheath. On supplying powdered carmine 

 to a living Caddis-worm, the presence of a current of 

 water, passing in at the head-end, is readily demon- 

 strated. A Caddis-worm, removed from its case, 

 performs undulating movements with its abdomen. 

 Other tube-dwelling larvae, .such as those of Chiro- 

 nomus and Paraponyx, maintain a current of water 

 in contact with their bodies in a very similar way. In 

 order to study the movements of a Caddis-worm 

 under something like normal conditions, I proposed 

 to Mr. Taylor to supply a naked Caddis-worm with 



^ This is the case with Phryganea grandis ; in some other 

 Caddis-worms the median tubercle is not more retractile than 

 the others. 



