461 



In this connection it is interesting to note that larvae of viridicollis 

 and decorus, which are blood-red and possess four long ventral respir- 

 atory organs, lohifcriis, which is blood-red and possesses two very 

 short ventral respiratory organs, and Protcnthcs cidiciformis, which is 

 whitish and has no ventral respiratory organs, were all commonly 

 represented in collections made in the Illinois River both in the por- 

 tions where the water is polluted by the Chicago sewage and where it 

 is comparatively clean. 



Various biological observations, and inferences and conclusions 

 based on them, have been published from time to time concerning this 

 insect and allied species, and two accounts of the latter class are now 

 briefly referred to in connection with kindred observations, offsetting 

 facts, and, in some cases, independent judgments of my own. 



A. B. Gahan has reported the occurrence of the larvse of Chiron- 

 omus dorsalis Meigen in a twenty-five-foot well, containing four or 

 five feet of water, at College Park, Md., during October and Novem- 

 ber*. 



Larvae captured from this well were placed in two beakers of the 

 well water, one containing the clear water, the other having placed in 

 it a little clay silt from the bottom of the well. Both lots of larvae sank 

 straight to the bottom of the beakers. Those in the clear water are re- 

 ported as thriving during the confinement. Concerning the others he 

 says : "Somewhat to my surprise, it was soon evident that those in 

 the beaker containing the clay were not prospering. Their constant 

 wriggling tended to draw them down into the mud, from which they 

 were unable to extricate themselves. At first it was thought that the 

 larvae were attempting to conceal themselves, but it soon became evi- 

 dent that this was not the case. The following morning all except 

 three or four of those in this beaker were found to be dead, having ap- 

 parently succumbed to suffocation." 



Observations made by the writer differ from the above in that the 

 observed larvae in almost every case burrowed into the mud or other 

 matter in the bottles or other receptacles in which they were kept. Ex- 

 perimental borings have proven that some of the "blood-worms" will 

 burrow twelve inches or more into the soft mud at the bottom of lakes 

 connected with the Illinois River; and borings made in 1914 in the 

 presence of the writer revealed larvae at a depth of eight inches in the 

 bottom of one of these lakes (Thompson's) near Havana. 



Gahan states, following Miall, that the larva of dorsalis is one that 

 is adapted to living in deep water, and that this is the reason why it 

 was brought up by the pump, the screen of the latter being near the 



*Proc. Ent. Soc. Wash., Vol. 14, 1912, p. 102. 



