4 BULLETIN OF THE BUREAU OF FISHERIES. 



they were living, and placed in shallow agateware trays. The debris containing the 

 larvae was usually spread out, so as not to be more than one-fourth of an inch deep, and 

 was then covered to a depth of half an inch with tap water. After a day or so, when the 

 larvae were especially numerous, as a rule they used all the loose debris in constructing 

 rather long U-shaped tubes, where they usually succeeded in maintaining themselves for 

 weeks at a time. The shallow agateware trays were rather generally used for the various 

 forms of larvae that could be collected in numbers. They are especially to be recom- 

 mended on account of the large amount of water surface exposed to the air, thus facili- 

 tating aeration. 



In breeding the various species collected a considerable number of individual 

 receptacles were required. In the early experiments square watch glasses with covers 

 were used successfully. They were later discarded in favor of medium-sized test tubes. 

 Such a tube with a cotton wool plug has numerous points of advantage over a watch 

 glass. First, the cotton plug permits a free exchange of gases. This circulation pre- 

 vents the accumulation of moisture on the inside of the test tube, so that the newly 

 immerged fly is not so liable to be caught in a water film and drowned. Second, the 

 cotton plug makes a very satisfactory surface to which a freshly immerged fly may 

 cling. Third, a number of test tubes may be placed together in a slanting position, so 

 that the water which they contain will expose a proportionally large surface to the air, 

 thus insuring perfect aeration. Fourth, a considerable number of tubes may be placed 

 in a tray and a uniform temperature maintained either by flowing water or by evapora- 

 tion from the surface of standing water. Fifth, the data concerning the larva may be 

 written on a small piece of paper and inserted with the cotton in the mouth of the test 

 tube. 



Mectriocnemus knabi larvae were kept for several weeks by bringing in the leaves 

 of the pitcher plant and placing them so that they would remain in an upright position. 

 They were kept full by the occasional addition of small amounts of water. The larvae 

 were also kept for weeks at a time in petri dishes containing the water and insect remains 

 obtained by emptying the leaves of the pitcher plant. They do not appear to be so 

 exacting in their environmental requirements as most chironomid larvae and can doubt- 

 less be reared in most any sort of a container. 



Chironomus lobijerus were brought into the laboratory in water-soaked Sparganium 

 stems, which were allowed to float freely in trays filled with water. In this condition 

 the larvae maintained themselves for considerable periods at a time. Upon removing 

 them from their burrow they were found to adjust themselves to various artificial 

 receptacles. The most satisfactory glass preparations for the observation of the habits 

 of Chironomus lobijerus larvae were constructed so as to give flat horizontal surfaces. 

 This was accomplished by cementing two rectangular strips of glass cut from cover slips 

 to either side of parallel capillary glass tubes. The size of the capillary tubes used was 

 slightly larger than the full-grown larva. 



It was found that King's "Microscopical Cement" is more satisfactory than a 

 cement made by dissolving asphaltum in turpentine or xylol, especially when it is 

 desired to make permanent mounts of the silken tubes. It is necessary to dehydrate 

 rapidly in order not to dissolve this cement, but even with this defect it is more satis- 

 factory than other cements soluble in xylol. Because of the uniform thickness and the 



