98 _ BRISTLE-TAIKS AND SPRING-TAILS. 
classification of insects (based on the principle of cephalization), 
and divided the Hexapodous insects into three groups: the first 
(Ptero-prosthenics, or Ctenopters) comprising the Hymenoptera, 
Diptera, Aphaniptera (Fleas), Lepidoptera, Homoptera, Trichop- 
tera and Neuroptera ; the second group (Ptero-metasthenies, or Ely- 
tropters) comprising the Coleoptera, Hemiptera and Orthoptera; . 
while the Thysanura compose the third group. Lubbock has given 
us a convenient historical view of the opinions of different authors 
regarding the classification of these insects, which we find useful.’ 
Nicolet, the naturalist who, previous to Lubbock, has given us the 
most correct and complete account of the Thysanura, regarded 
them as an order, equivalent to the Coleoptera or Diptera, for ex- 
ample. In this he followed Latreille, who established the order in 
1796. The Abbe Bourlet adopted the same view. On the other 
hand Burmeister placed the Thysanura as a separate tribe between 
the Mallophaga (Bird Lice) and Orthoptera, and Gerstaecker 
placed them among the Orthoptera. Fabricius and Blainville - 
put them with the Neuroptera, and the writer, in his ‘ Guide to 
the Study of Insects,” and previously in 1863, ignorant of the 
views of the two last named authors, considered the Thysanura as 
degraded Neuroptera, and noticed their resemblance to the larve 
of Perla, Ephemera, and other Neuroptera, such as Rhaphidia and 
Panorpa, regarding them as standing “in the same relation to the 
rest of the Neuroptera [in the Linnean sense], as the flea does to 
the rest of the Diptera, or the lice and Thrips to the higher Hem- 
iptera.” 
After having studied the Thysanura enough to recognize the 
great difficulty of deciding as to their affinities and rank, the writer 
does not yet feel prepared to go so far as Dana and Lubbock, for 
reasons that will be suggested in the following brief account of 
the more general points in their structure, reserving for another 
occasion a final expression of his views as to their classification. 
The Poduridee, so well known by name, as affording the scales 
used by microscopists as test objects, are. common under stones 
and wet chips, or in damp places, cellars, and about manure heaps: 
They need moisture, and consequently shade. They abound most 
in spring and autumn, laying their eggs at both seasons, though 
most commonly in the spring. During a mild December, such as 
just experienced, they may be found in abundance. Nearly ® 
dozen species were found on the grounds of the Museum of the 
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