174 Annals Entomological Society of America [Vol. IX^ 



feeding was confined largely to adjacent leaf tissue not a part 

 of the case itself. All excrement was voided outside of the case, 

 thus providing for the cleanliness of the interior. 



Forbes ('10, p. 220) states that in addition to NymphcEa, 

 Castalia and Brasenia are used by TV. macidalis in case-making 

 and his description leads one to infer that all of these plants 

 are used as food. The writer has found no evidence of feeding 

 or case construction involving plants other than N. america?ia 

 although Nymphcea and Castalia intermingle in, the same beds. 

 Brasenia does not occur in the Douglas Lake region. 



■ Respiration. — Respiration in the first instar is apparently 

 cutaneous. Tracheal gills have not yet appeared and, since the 

 larva is almost constantly submerged, it would appear that it 

 must of necessity utilize the dissolved oxygen of the water by 

 absorption through the body-wall. Larvae, hatched and reared 

 in the laboratory, almost invariably sought the lower side of the 

 water-lily leaf regardless of whether the leaf was submerged or 

 floating. A study of the various situations in which the larvae 

 of N. maculalis occurred most abundantly showed that the 

 water contained a considerable amount of dissolved oxygen, due 

 to the exposure to the air and the agitation by wind and wave 

 action. It is possible that the oxygen demands of the larva in 

 the first instar are low enough that they can be satisfied by the 

 cutaneous form of respiration and special organs are not 

 demanded. 



After the first ecdysis, tracheal gills appear, each gill con- 

 taining a primary branch from the longitudinal tracheal trunks. 

 The appearance of about fifty gill filaments in the second instar 

 would seem to be ample provision for the increased oxygen 

 demand. The marked increase in the number of gills and in 

 the number of branches of each gill in the later instars has 

 been discussed. 



The occasional appearance of larvae on the upper surface of 

 the leaf seems to indicate an ability to pass at least a limited 

 time out of water. Instances of pupation on the upper surface 

 of the leaf were observed in the field and the time required for a 

 larva to emerge from the water, locate the case, and construct 

 the silken inner covering would seem longer than the individual 

 could survive without some form of oxygen supply. No data 

 were secured on the mode of respiration under these conditions. 



