AQUATIC MIDGES AND SOME RELATED INSECTS. 33 



Taylor's observation upon the use of evacuated Spirogyra filaments in the construc- 

 tion of the tube is quite correct for Trichocladius nitidellus, as is also his observation of 

 the use of silk to fasten the fragments together. "Fibrous structure," which Taylor 

 saw only "faintly," was not noticed. 



The larva carries on its respiration in the usual way, but since it habitually lives in 

 a well-aerated environment it lacks haemoglobin in its blood and simply takes the color 

 of the food contained in its stomach. Such larvae characteristically have much better- 

 developed tracheal systems than those provided with haemoglobin. This fact, together 

 with Taylor's drawing (Miall and Hammond, 1900, p. 15, fig. 8), which shows a well- 

 developed tracheal system, tends to corroborate his identification to the genus Ortho- 

 cladius to which all the species of Trichocladius were formerly referred. 



The available literature on the feeding habits of all the Orthocladius larvae is so 

 limited that it is impossible to tell whether any considerable number feed upon different 

 filamentous algae or not. It seems probable that the specimen observed by Taylor and 

 assigned to this genus is either identical or closely related to Trichocladius nitidellus. 



Group VI. 



This group or subdivision of the Chironominae is erected to include several species 

 known to live throughout the larval stage without building any semblance of a tube. 

 Since there are several genera represented by these forms which have relatively little 

 more in common than their free living manner of life, the author has divided them 

 into subgroups based upon the structure of their mouth parts and the nature of their 

 habitats. 



Group VI: Subgroup A. — Metriocnemus knabi Coquillett. 



These larvae are quite unique in their habitat, food, and manner of life. They were 

 apparently first studied in the larval condition by Rnab (1905), who made a number of 

 observations on the larvae and pupae. He found them in the pitchers of the pitcher 

 plant (Sarracenia purpurea), and, so far as known, the larvae are not found in any other 

 habitat. Although confined apparently to a single limited habitat, they are evidently 

 widely distributed, for Knab found them at Westfield, Springfield, and Wilbraham, 

 Mass., and at Cedar Lake, 111. The writer has found them at McLean, N. Y., and they 

 are doubtless to be found wherever Sarracenia purpurea occurs. 



The larvae of the present species live at the bottom of the water-filled leafcups of Sarracenia pur. 

 purea, burrowing in the closely packed debris composed of the fragments of decomposing insects. Evi- 

 dently their food is from this source. [Knab, 1905.] 



HEAD STRUCTURES. 



The head structures for this subfamily have already been discussed, but this par- 

 ticular species and doubtless the entire genus (for the larval stage of very few are known) 

 show decided modifications in their mouth parts. These modifications are well adapted 

 to the present mode of life of the larvae. 



The labrum has the usual epipharyngeal comb well, though not strongly developed. 

 It also has the labral comb well developed, very wide, and finely toothed. The usual 

 hooks, pectinate hairs, and spines are present, but somewhat modified. The pectinate 

 hairs are here quite broad at their tip and furnished with a straight and uniformly 



