OXYGEN SUPPLY OF CERTAIN ANIMALS 299 



lake, constructing tubes for themselves from small particles of 

 organic debris and mud, the whole being cemented together 

 by a secretion from their spinning glands. They remain in these 

 tubes the greater part of the time, coming out occasionally to 

 crawl over the surface of the mud for short distances, but soon 

 burrow again. This fact was determined by observation of 

 specimens kept in the laboratory under conditions as near 

 normal as possible (Appendix, p. 318). The larvae of C. tentans 

 are scavengers, their food consisting of mud containing small 

 particles of organic material. 



Chironomid larvae normally respire through blood-gills located 

 on the last two segments of the body. The posterior part of the 

 body keeps up rhythmical undulating movements which insure 

 a continual fresh supply of water. Such movements continue 

 when little, or even when no oxygen is present. Maill and 

 Hammond ('00) state that the larvae of Chironomus dorsalis 

 and Chironomus plumosus, large species which they studied, 

 came to the surface when the oxygen supply was low to bathe 

 their bodies in well aerated water. Such behavior has never 

 been observed by the writer in connection with the larvae of 

 C. tentans, either when the larvae were confined in oxygen-free 

 water or kept in open jars in the laboratory. Furthermore, the 

 limited swimming ability of this larva makes it highly improbable 

 that those living at any considerable depth in the lake would be 

 able to come to the surface or even travel very far in that 

 direction. 



The gills of the larvae of Chironomus tentans, which are merely 

 outpocketings of the body wall, contain sinuses of the circulatory 

 system and are continually filled with an ever-changing supply 

 of blood. Oxygen, therefore, can be easily transferred from the 

 water through the delicate gill membrane to the blood within. 



The blood of the larvae of most species of the genus Chiro- 

 nomus .contains haemoglobin, and therefore has a character- 

 istically red color. Rollett ('61) was the first to show that the 

 red pigment was haemoglobin. He obtained haemoglobin 

 crystals and also showed that the blood was dichloric — that it 

 gave a red color when light passed through a thick stratum, but 



