AQUATIC MIDGES AND SOME RELATED INSECTS. 37 



processes resembling those observed in Metriocnemus knabi. The hypopharynx also 

 suggests that of M. knabi and doubtless shows a close generic relationship. 



The structures referred to above as not having their homologies well established 

 are those to be found on the ventral side of the head (fig. 32, c), and suggest at once 

 the fan-shaped membrane which the writer has labeled c in figure 11. Mundy (1909) 

 has observed and mentioned these structures. He also gives a figure (PI. V, fig. 18) 

 and states that it is his opinion that the long filaments which the author has shown in 

 figure 32 doubtless fuse and form the fanlike membrane which is so characteristic of 

 the genus Chironomus. The author has been unable to establish the connection between 

 these structures and the articulation of the maxilla shown in figure 1 1 and is therefore 

 doubtful about their identity. The other mouth parts are very similar to those given 

 for Chironomus brasenice and therefore need no special mention. 



FEEDING HABITS. 



The feeding habits, judging from the food found in the stomach, involve a process 

 of selection. The larvae, as indicated above, creep along through the trash at the bot- 

 tom of streams and consume whatever they encounter that seems most edible. Those 

 examined had a considerable quantity of plant fragments and some soft, brown unrecog- 

 nizable substance in their alimentary canal, but no diatoms were found. It was 

 suggested by Mundy that the vibrissas on the ventral side of the head of this larva 

 might serve as the vibrissa? on the sides of a cat's head. It seems probable to the writer 

 that their function is a tactile one. They doubtless enable the larva to distinguish 

 the different substances which are more or less edible and in this way supplement the 

 more delicate sense structures within the head of the larva. 



The group as a whole contains larvae with mouth parts that allow greater freedom 

 of movement, especially in connection with the maxillae, than in any of the other groups. 

 Associated with this modification of the maxillae is the entire lack or slight development 

 of the fanlike membrane on each side of the labrum. The hypopharynx seems to be 

 developed as a more efficient organ of sense and doubtless serves an important function 

 in the selection of the food. The other structures of the head are in general similar 

 to those characteristic of the previously discussed groups. It seems probable from the 

 structure of the mouth parts that this is the more primitive group, as Goetghebuer has 

 also suggested. The free-living habits of the larvae seem also to supplement this 

 conclusion. 



SUBFAMILY TANYPINjE. 



This subfamily contains seven genera, and at least 45 species are known to occur in 

 North America; but in spite of the number of known adults the author has failed to 

 find any considerable literature bearing on the larval habits. Fr. Meinert (1886) made 

 a number of observations upon a Tanypus species which he figures. These observations 

 have been followed quite closely by Miall and Hammond (1900) and Johannsen (1903). 

 This literature while good as a general treatise fails to give any very adequate idea of the 

 feeding habits beyond the statement that the larvae are predacious. Miall and Hammond, 

 however, state : 



Bloodworms are preyed upon by many aquatic insects as well as by fishes. Caddis worms, Perla 

 larvae, Sialis larvae, and Tanypus larvae devour them greedily. A number of empty heads of the blood- 

 worms may often be seen in the stomachs of a single Perla or Tanypus larva. 



