ANATOMY AND PHYSIOLOGY. 101 
really nothing to do with digestion; ther proper 
function is to secrete silk or mucus, to form the 
cocoons of the pups, or the nests of the perfect 
insects. The nature of the secretion differs not only 
in different insects, as we might have expected, but 
in the same insect at different periods of life. To 
take a few familiar instances. The frothy fluid with 
which the honey-bee kneads her wax plates till she 
has formed them into a paste of a proper consistency 
is derived from the salivary glands. So is the well 
known substance of which silk-worms make their 
cocoons. Probably the caddis-worm derives the 
hydraulic-cement with which she fastens her build- 
ing materials together, from the same source. The 
poison which biting insects—biting in the domestic, 
not the entomological sense—inject into the wound, 
is also a secretion of the salivary glands. 
The spider takes rank next to the various species 
of silk-worms as a silk-manufacturer. But they do 
not secrete it from their salivary glands, which have 
quite a different function. The spider’s spinneret 
opens on the outside of the abdomen by numerous 
orifices, and the separate strands do not coalesce 
into one thread till they reach the open air, instead of 
within the ducts of the gland. This makes the 
thread of the spider appear of a more complex and 
elaborate structure than the silk-worm’s, but it is 
not necessarily so. It would seem to hold a middle 
place between that of the silk-worm and the wasp in 
the rapidity with which it takes a solid form. The 
thread issues ready formed from the mouth of the 
silkworm. In the spider’s thread the drying process, 
however instantaneous, requires the access of the 
