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N. E. McINDOO 



on the first segments are long and rather stout (fig. 22) ; they are 

 not innervated. On the last segment two types of pegs were 

 found; one type arises from pits and the other type from thin 

 chinitous plates. Of the first type only one hair was observed 

 (fig. 30, THr), but a bunch of hairs belonging to the second type 

 was found at the extreme tip of each antenna, maxillary palpus and 

 labial palpus (figs. 28 and 29, Pg). Each bunch of hairs arises 

 from the center of a thin, transparent plate. On the antenna the 

 bunch consists of about 5 hairs (figs. 24 and 31, Pg)', on the 

 maxillary palpus of about 12 hairs (fig. 32) ; and on the labial 

 palpus of about 9 hairs (fig. 33). The walls of these hairs are 



31 

 Figs. 31 to 33. Disposition of olfactory pegs {Pg) and single olfactory organ 

 at tips of three head appendages, X 320; fig. 31, dorsal surface of antenna; figs. 

 32, dorsal surface of maxillary palpus; and fig. 33, ventral surface of labial palpus. 



comparatively thick, and for this reason such organs are not well 

 adapted to receive chemical stimuli, nevertheless Nagel (94) 

 called them gustatory organs in the larvae of Dytiscus marginalis, 

 for he asserts that these larvae are able to distinguish meat from 

 filter paper only after having brought these hairs into actual 

 contact with the objects dropped into the water. Being igno- 

 rant of the location of the olfactory pores in these larvae, Nagel 

 naturally assumed that these hairs are organs of taste ; neverthe- 

 less, it seems more reasonable that aquatic larvae can distinguish 

 food only by actually coming into contact with it, for water is 

 perhaps a poor medium for the distribution of odors. 



