Odonata 271 



earlier months, Lemna later) was kept growing. Through the nearly 

 three years during which the rearing of N. bella was carried on, the dishes 

 containing the larvae were kept on the inner sill of a window facing 

 north. The temperature of the room, as indicated by a self-recording 

 maximum and minimum thermometer, ranged from 89 to 50 F. (31. 6° 

 to io° C). 



In December, 1925, each of the four living larvae, then somewhat over 

 2 mm. long, was transferred from the salt cellar to a glass "caster cup 1 ' 

 having a capacity of 15 cc, with the water and other contents in which 

 it had been living previously. In June, 1926, each was again transferred 

 from the caster cup to a finger bowl. Each caster cup and finger bowl 

 was kept constantly covered with a piece of glass. 



In June, 1927, when the first of the N. bella larvae gave indication, by 

 the whitening of its eyes, that transformation was approaching, its 

 finger bowl was placed uncovered in a cylindrical glass battery jar. In 

 the finger bowl was put a stick of wood so placed that it extended below 

 the surface of the water; its upper end rested against a strip of wire 

 netting attached to a framed window screen in front of a closed window 

 facing south. Thus was provided a place for transformation. 



One larva, from the same lot of eggs, lived for another year, until June 

 1928, before it transformed. 



When the larvae were about one week old drops of a culture of 

 Paramecium were placed in the vessels in which they were living. [For 

 culture see pp. 1 12-128.] Soon after, other Infusoria, small copepods, 

 ostracods, rotifers, larvae of Anopheles, and other organisms smaller 

 than N. bella were added. For nearly a year from Sept. 19, 1925, the 

 food supply was chiefly small Crustacea, some of which bred in the dishes 

 containing N. bella. In August, 1926, chironomid and ephemerid larvae, 

 in September and October 1926, corixid and culicid larvae were given in 

 addition. In late February, 1927, mayfly larvae were more frequently 

 furnished; although these were taken from a swiftly flowing stream they 

 lived in the absolutely still water of the dish for at least eight days and 

 possibly longer. Similar observations were made in connection with other 

 mayfly larvae, those of the genus Heptagenia being much more able to 

 survive in still water than those of Baetis, for example. 



Special attention was paid each day that the N. bella larvae were 

 examined to noting whether any possible living food material had sur- 

 vived from the previous week and in only three cases was an entire lack 

 of such found. The slow rate of development of the larvae may not, 

 therefore, be ascribed to absolute starvation, although it is of course 

 possible that the optimum food was not in the dishes. The hairs on the 

 body of the larvae are fairly dense, and to them vegetable debris usually 

 adhered to such an extent as to hide the body surface. This mass which 



