1883.] NATURAL SCIENCES OF PHILADELPHIA. 219 



they are found more or less in societies, on tree-trunks, palings, 

 amongst the herbage of trees, and even in houses. Mr. Aaron dis- 

 covered them in similar habitat here, that is to say on the trunks 

 of trees. A congener of the above species, Psocu>i purus Walsh, 

 which is also found in the vicinity', makes a tubular or tent-like 

 web in the farrows of bark and crevices of trees, in texture some- 

 thing like that spun b3^ certain tube-weaving (Tubitelarise) spiders 

 and other species ; or, perhaps more nearly like the covering 

 woven over themselves by certain Lepidopterous larvaj. The 

 insect lives under this tent precisely as do the spiders referred to. 

 One who would capture them must push them out by pressing 

 upon the tent. 



It is a matter of such rare interest to find a true insect in the 

 imago state spinning a web, and apparently for its protection, 

 that Dr. McCoolc thought the discovery in our locality of such 

 an insect worthy of this record. The spinning function among 

 true insects, he believed, with the single exception of the Psocidte, 

 is confined to tlie larval state ; spiders (it is scarcely necessary to 

 state) not being true insects, but belonging to the Arachnida. 

 The speaker further thought that this larval characteristic of 

 web-spinning might be correlated with the rank which zoologists 

 usually assign the Neuroptera as lowest among the orders of the 

 insects, its larva-like body being one indication of its low position 

 in its class. However, it is a striking example of the diverging and 

 independent lines along wliich life-torms iiave sprung up in nature, 

 that a function which belongs to the larval stage of insects, and 

 which appears in the imago state only in the lowest type of tiie 

 same, should appear as the most permanent and characteristic 

 function of the spider — an animal which, although it is now 

 commonly given a lower place in the same subkingdom with the 

 insects (Arthropoda), is certainl}- very differently and little less 

 highh' organized. It would be a difficult task. Dr. McCook 

 thought, to trace or even imagine an}' evolutionary connection, 

 whether of progression or retrogression, between the web-spinning 

 spider, the web-spinning insect-Uirva, and the web-spinning neu- 

 ropterous imago Psocus Hexpunvtatus. There is, indeed, this 

 common factor, the spinning function, but the phj^siologist fails 

 to perceive any use or combination of the same which can unite 

 the organisms in which it inheres. 



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