4 2 



"boss" has usurped the function of the bifurcators and checks the 

 larva from going out too far. Similar but larger bosses are described 

 by LAUTERBORN in two out of his three case-builders, and they may 

 be the means by which these larvae are retained in their cases. Lastly 

 there is LAUTERBORN'S Larva 3, which makes a truncated case, in which 

 it moves about. It resembles C. pusio closely in its anatomy and 

 possesses bifurcating hairs. A function, such as I am arguing for the 

 bifurcators, would be of considerable use to this larva in crawling about 

 as it has no sensitive boss to check its movements. I have not found 

 the species and DR. LAUTERBORN does not mention this point in his 

 paper, so I cannot say whether or not the habits of this larva are 

 favourable to the bifurcator control theory. 



Many other animals besides the Chironomids make cases in which 

 they dwell and in which they often crawl about, as, for instance, the 

 Trichoptera. Many of these larvae have fleshy prominences on the 

 first abdominal segment and a fringe of black hairs running along each 

 side of the body. It has been suggested that the prominences steady 

 the larva during the undulatory movements kept up by the abdomen 

 for respiratory purposes.* Possibly they also help the larva to hold on 

 to the case when crawling about. 



More important for us are the lateral fringes of hairs. These may 

 on the principles already indicated be sensitive hairs with a pleasurable 

 feeling-tone, and thus act in the same way as the bifurcators of C. pnsio, 

 and check the larva from passing too far out of its case. It is to be 

 noted that they are much larger in young larvae than in those that are 

 full grown (I have noticed the same comparative difference in size between 

 the bifurcators of the second and fourth instars of C. pusio). This is quite 

 in accordance with psychological principles, for until the habit has been 

 formed the stimulus must be strong, but after the habit has become 

 deeply ingrained in the organisation, secondary associations have sprung up 

 and the primary stimulus need not be so great, and is often entirely absent. 



Prof. A. JAMES shows that the habit of walking originates in this 

 way, for he writesf : " Until the impulse to walk awakens by the 

 natural ripening of the nerve centres and sensory nerve termini, it seems 



* MIALL Aquatic Insects, p. 247. 

 f Principles of Psychology, vol. II., p. 405. 



