heal iil 
—— =. 
NEST MAKING: ITS ORIGIN AND USE. 333 
The material which is fastened upon the internal silken sack consists 
of particles of the food plant upon which the caterpillar is reared. These 
are the stems and other rejected portions of the plant, left when feeding, 
and which hang to the silken bag on the outside. They are sometimes so 
_ thickly placed that the silken sack is entirely covered, as at Fig. 325, 
which is a specimen from the Southern States in my collection of insect 
architecture. 
One might extend these comparisons much further and find that the 
striking resemblances between the protective architecture of spiders and 
; that of the larve of insects might be carried to the very lowest 
ead forms of life. Prof. Joseph Leidy, in his monumental work 
upon the Rhizopods,! has presented numerous forms of these 
creatures, that lie so far down in the scale of animated being, which at 
once call to mind the habits of the caddis fly larva and the larva of the 
house builder moth. Fig. 326 represents the Rhizopod, Difflugia urceolata, 
a common form found in ditches in the neighborhood of Philadelphia. 
Ordinarily the shell of this Difflugia strikingly resembles the ancient 
Roman amphora. The body of the shell varies from a globular shape to 
a more or less ovoid form; the principal extremity or fundus is more ob- 
tusely rounded, or more or less acute; and sometimes it is rounded and 
more or less acuminate. The shell is composed, as is generally the case 
in other species of the genus, of colorless angular particles of quartz sand, 
mostly of larger ones scattered with more or less irregularity, while the 
intervals are occupied with smaller ones. Frequently larger stones occupy 
the larger shell; but, passing this, they gradually become smaller, approach- 
ing the edge of the rim or reflected lip.? 
Another Rhizopod which suggests at once the architecture of the bag 
worm is represented at Fig. 327. Difflugia acuminata is one of the most 
common forms of Rhizopods, and is very generally distributed. Not un- 
frequently, as in the figure, the shell is composed of colorless, chitinoid 
membrane incorporated with quartz sand, alone or with this and intermin- 
gled diatoms. In this the grains of sand are usually closely placed in jux- 
taposition at and near the mouth of the shell, but are elsewhere scattered 
and separated by wide intervals. In some cases the shell is more or less 
covered with large diatoms, which are generally adherent in the length, 
and diverge upward beyond the boundary of the shell.? 
Not only do we find these striking resemblances in the external archi- 
tecture of these widely separated creatures, but apparently we find the 
same purposes originating the architecture. The house builder moth larva 
constructs her thatched domicile in order to cover over its soft body ; 
*“Fresh Water Rhizopods of North America,’ Washington, 1879. 
2 Op. cit, page 107, and pl. 14, Fig. 3. 
’ Leidy, Idem, page 111, pl. 18, Fig. 21. 
