The bifurcators are therefore responsible for (i) the stay-at-home 

 habit, (2) the habit of never exposing the last four segments, (3) the 

 length of the arms of the case, (4) the length of the case (in Chironomus 

 No. i). 



If the above mentioned characteristics are the result of the presence Negative evidence. 

 of the bifurcators, then a larva similar in all other respects to the full- 

 grown C. pusio, but lacking these organs, would be expected to manifest 

 none of these characteristic habits. The nearest approach to this 

 desired similarity is to be found in the newly-hatched larvae of C. pusio, 

 which have no bifurcating hairs until after their first moult. 



These minute larvae are very restless in their habits, continually 

 leaving their tubes before they are completed, so that few remained 

 long enough to complete a five-armed case, and whenever I examined 

 the aquarium in which they were kept some were always to be seen 

 swimming about freely in the water. Concerning one that made a 

 well-finished case, I have made a note to the effect that the arms 

 were about as long as the case and the case about as long as the body ; 

 hence in the absence of bifurcators these larvas must venture to expose 

 the whole length of their bodies during arm construction (I regret that 

 I can give no measurements, but I have been unable to procure eggs 

 or young larvae since I have realized the importance of this point). 



I must now say a few words about the other larvae which bear 

 bifurcating hairs. What has been said about C. pusio applies equally 

 well to the Stalk-cased Larva No. i. Larva 4 and Larva 6 I have not 

 observed, while Larva 3 appears to act in the same way as C. pusio, 

 but as it has no arms measurements cannot be taken. The Pipe-larva 

 No. 5 possesses the hairs but they are much smaller in proportion to 

 the large size of this species and very often much broken, so that I 

 doubt if they are functionally active, at any rate in the full-sized larva. 

 I have observed that at night they extend far out of their tubes 

 exposing almost the whole body, often (I should say) overstepping the 

 ninth segment. A small smooth and transparent prominence arises in 

 the mid-dorsal region of the eleventh segment, and this and the two 

 adjacent segments are very much flattened out. I conclude that this 



Bifurcator control 

 in other larva;. 



