1937] Case-building Instinct of Trichoptera 127 
we have no new observations on this part of the process. 
Each piece of plant material is taken by the larva, smeared 
with the salivary secretion and set in place. As the case is 
extended, the original girdle and the completed part of the 
case are moved backward so that they cover the abdomen. 
The end to which new material is being added stays in the 
same position where it is easily reached by mouth-parts and 
legs. By the addition of material at the forward end the 
case is eventually completed. 
Observations were also made on case-building in Molanna. 
Using sand grains these larvae build cases consisting of a 
central cylindrical tube, having at the anterior end a broad 
extension or overhanging hood that protects the animal from 
above even when its head and thorax are projected from the 
tube proper. This broad hood extends backward on either 
side of the main part of the case and forms lateral flanges 
possibly useful in preventing the case from rolling on its side. 
The typical case-building procedure of a Molanna larva 
when pushed from its case and supplied with sand to the 
depth of about a centimeter is as follows. For about a minute 
the larva crawls about over the sand. It then curls its 
abdomen downward so that it no longer moves forward even 
though it continues to move its legs. This results in the dig- 
ging of a slight pit in front of the larva and in the formation 
of a pile of sand beneath the body. Presently the head is 
forced down into the pit and turned underneath the pile of 
sand and underneath the body of the larva. Thus the animal 
is curled and lies on the back of its head as in the first step of 
a somersault. It then digs farther into the sand, joining the 
sand grains together loosely with the salivary secretion. Its 
head finally emerges at the surface on the side of the small 
pile of sand where the abdomen was located when the process 
began. The larva at this point has nearly completed a 
somersault and lies on its back in a sort of tunnel beneath 
the pile of sand. It next joins together the sand grains 
around the opening of the tunnel. When the sand grains 
which line the entrance to the tunnel have been firmly ce- 
mented together the animal is encircled by a firm girdle. As 
in the limnephilid, this is the foundation to which further 
building material is added to effect the completion of the 
case. In Molanna the girdle may be completed within fifteen 
