AQUATIC MIDGES AND SOME RELATED INSECTS. 5 



flatness of the surfaces (fig. 26) this type of glass preparation is more satisfactory than 

 any flattened tube the author was able to manufacture. 



Ehrlich's acid hematoxlin was found to be the most satisfactory of any stain used 

 for bringing out the silk structures. "Licht green" and "eosin" were also used but 

 were not found satisfactory. The licht green, while staining the silk glands and the 

 silk within the silk duct, did not stain the silk outside of the body. The eosin, while 

 staining the silk slightly, was found unsatisfactory because of the ease with which it was 

 removed in dehydration. 



There are few animals that lend themselves more readily to a laboratory or lecture 

 demonstration than do these stem-dwelling larva?. They seem to differ decidedly from 

 other chironomids, especially those that characteristically live in a mud burrow, in 

 their reactions to strong light. Their greater tolerance of light enables one to demon- 

 strate the silk-spinning movements and- the general behavior of the larva by means of 

 a stereopticon. The only requirements are that the larva? shall have recently built a 

 fresh, clean silk tube in a glass preparation, and that the temperature of the water be 

 kept down to normal room temperature. The reason for requiring that the silken 

 tube be a fresh one is that after a week or two the silk becomes much discolored by the 

 lodgment of fine particles as well as by the deliberate attachment of masses of castings 

 to the ends of the burrow. It is only necessary to remove the larva by a jet of water 

 and then the tube can be removed by a needle. A few hours will usually suffice to 

 enable them to again replace the silken tube. The temperature is easily controlled by 

 having a specially constructed lantern slide through which a current of water can be 

 made to pass. A type used with considerable success was constructed as follows: 



Two pieces of sheet brass the size of a lantern slide were cut so as to give a sym- 

 metrically placed rectangular opening \ x ,i by 2 inches near their center. These two 

 brass strips were drilled and fitted with screw bolts. Two sheets of transparent celluloid 

 and a single sheet of rubber packing material about an eighth of an inch in thickness 

 were punched so that the holes coincided with those in the brass plates. The rubber 

 packing was cut so as to give a rectangular opening which coincided with that in the 

 brass plates, and the parts were assembled in the following order: Sheet brass, celluloid, 

 rubber packing, celluloid, and brass. Two one-eighth-inch rubber tubes were connected 

 with the inclosed chamber by openings at diagonally opposite corners. It was found 

 easier to make this connection through one of the sheets of celluloid than through the 

 rubber packing material. These tubes were fused in with beeswax and their ends 

 weighted and put into separate jars. The tube opening at the bottom of the lantern slide 

 was used as the intake tube and the jar to which it was connected was filled with cold 

 water. Then by gravity the water was made to flow through the chamber. Two adjust- 

 able pinchcocks were provided and the flow of water stopped while the glass prepara- 

 tions containing the larva? were being placed in the chamber. Then by regulating the 

 flow of water by means of the pinchcocks the preparation was used as long as desired. 

 When the water had all been passed through, the jars were changed and it was sent 

 through a second time. It was found desirable to have the water removed from the 

 top of such a chamber on account of air bubbles which tend to accumulate when well- 

 aerated water is heated slightly. 



