yS FIELD AND FOREST. 



being refractory in confinement, Luna secreting a much smaller quan- 

 tity of dark-colored material, an(\ Fi'-omefhea having the peculiar habit 

 of woolding its very fine thread around the twigs of the trees on 

 which it feeds, while Polyplievius alone has proved docile in confine- 

 ment, and, although producing a coarse thread, the most valuable for 

 many purposes. The thread differs from most other fibrous substances 

 in its microscopic characters only in being of exceedingly variable 

 diameter, this depending largely upon the rapidity with which it is 

 extracted from the body of the insect at different periods, and in be- 

 ing thoroughly homogeneous, translucent, and without texture, while 

 the web or thread of the spider, issuing from thousands of minute ori- 

 fices, termed spinnerets, situated in a quincuncial form on the under 

 surface of the spider's abdomen, is a compound thread of which the 

 component filaments are readily distinguishable under the microscope. 

 Beside the Lepidopfera vaany of the families of \\\t Hymenoptera 

 spin or weave a more or less tough and substantial cocoon, some, as 

 Gruptits and Ophion, even spinning their own tough cases, while per- 

 fectly protected by the still tougher coating of the Pro7>iethia' s or 

 Cecropia^s cocoon. ^The saw-flies' cocoons are generally of thinner 

 and brittler character than those of the IcJincmnons. Those of the 

 Pelopoeus and some other Sphegedce are still thinner anti more brittle, 

 but encased in a solid wall of mud-cement, not unfrequently half an 

 inch in thickness. 



Some at least of the Pscndo-ncuroptcra spin from a tubule on the 

 under surface of the last segment, reversing the position of the orifice 

 from that of the Lepidoptcra. 



The greater portion of tht Psei/do-iieuropfcra spin a silken elongated 

 cocoon, which is still further protected by the incorporation therewith 

 of small twigs, bits of grass, fragments of leaves, or pebbles and grains 

 of sand. This cocoon, open at one end, is inhabited bv the larva, 

 which drags it from place to place, protruding its head and six slender 

 feet from the open end, while its curved pro-legs securely clutch the 

 silk at the other extremity. At the approach of its pupal transforma- 

 tion it builds a fine lattice-work of silken fibre across the heretofore 

 open passage, and passes into the pupa state. 



F. G. Sanborn. 



