33 



much shorter, never reaching the head and first nine segments in 

 length : the psychological reason for this will be made plain later on. 



On the other hand the length of the stalk is very variable, Length of stalk, 

 depending simply upon the time that the larva chooses to continue 

 robbing the bottom to add to the top ; such wide differences in length 

 as from i to 4 mm. may be met with. There now remains only the 

 construction of the three arms ; at first they are made at the expense 

 of the lower end of the tube, but as soon as they are a millimeter or 

 so in length, webs are stretched across, and soon a supply of building 

 material is at hand to finish the work without having recourse any 

 longer to the parsimonious habit I have just described. 



To build the arms the larva collects a mass of particles into a 

 small lump and applies it to the rim of its case and continues placing 

 nodule upon nodule to the free end until the arm is the required 

 length. During the construction of the arms, as well of the case and 

 stalk, after putting a nodule in position, the larva makes a number of 

 rapid movements whereby the material is smoothed and plastered down, 

 and saliva poured into the crevices between the particles. In strengthen- 

 ing an arm the larva will twist its head right round it describing thereby 

 a complete circle, completing the forward and return movement with 

 the greatest rapidity. In fact ail its movements are performed in what 

 appears to be a feverish state of excitement, in which the antennae 

 partake, with their perpetual interrogation by rapid vibratory movements 

 of every object within reach, and it seems certain that these organs 

 must be highly sensitive, in spite of the small size of the sensory bulbs 

 they bear. Only when retired within its case, so that the head alone 

 appears, does the larva become at all quiet ; and in this position it is 

 well protected from danger. 



The arms as before mentioned are connected by webs so as to form The net. 

 a net to retain all passing objects, but even with a high power lens I 

 have been unable to detect single threads, the net-work seems only to 

 be made up of irregular bands of slime or mucus passing between the 

 neighbouring arms, so probably it issues from the creature's mouth in 

 this form. 



