130 
Psyche 
[December 
failing will make another chain, or add to the same one and 
then again “endeavor” to complete a girdle. It does not, 
however, cut the pieces to a length which would permit their 
effective use. With 3.5 mm. bits a girdle may be completed. 
Larvae supplied with a mixture of long and short pieces use 
both to make the chain of material that precedes the forma- 
tion of the girdle, but because this contains some long ones 
they are unable to wrap it around themselves to complete it. 
We found no evidence of a selection of material during the 
early steps in case formation when the length of the pine 
needle fragments was the only varying factor. Gorter 
(1929, p. 92) in the limnephilid that he studied observed 
that : “In the construction of the provisional tube all kinds 
of material were employed by the larvae, but the pieces could 
not be too large, for the larva did not bite the material into 
smaller pieces during the provisional building-process. Bit- 
ing takes time and during the provisional building-process 
the larva makes the impression of being in a great hurry. 
Speed is the chief thing, not firmness, as with the final 
structure. . . .” 
These observations clearly indicate that during girdle 
formation there is little or no selection and no cutting of 
materials, but that later when the case is partly cpmpleted 
there is both selection and cutting. However, if the choice 
during the early steps lay between flexible and stiff material 
the animals might have shown some selection, for Gorter 
(p. 92) observes: “In the provisional building-process one 
thing was very remarkable: there was a great preference 
for algae, a flexible and soft material, which can be quickly 
wrapped around the larva without being bitten off.” We 
have not tested this point. 
No thorough tests were made to determine whether 
Molanna would show selection of building materials during 
the early stages when it works rapidly. However, as the 
case nears completion and the animal works more slowly 
there is evidence of selection. 
Examination of cases of Molanna shows that the sand 
grains of the tube are more varied in size than those of the 
flange and hood. The latter are nearly all relatively large 
grains. In one instance in which a larva had been supplied 
with a mixture of glass and sand the result was a completed 
case almost all of sand but with some glass in the older part 
