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Now such forms as these Thysanura, together with the mites and the singular Pauropus, we cannot avoid suspecting to have been among the earliest to appear upon the earth, and putting together the facts, first, of their low organization; secondly, of their comprehensive structure, resembling the larvæ of other insects; and thirdly, of their probable great antiquity, we naturally look to them as being related in form to what we may conceive to have been the ancestor of the class of insects.
The Abbe Bourlet, Templeton, Westwood, and Haliday have published important papers on the Thysanura; and Meinert, a Danish naturalist, and Olfers, a German anatomist, have published important papers on the anatomy of the group.
The eggs are laid few in number, either singly or several together, on the under side of stones, chips or, as in the case of Isotoma Walkerii, under the bark of trees. They are round, transparent. The development of the embryo of Isotoma in general accords with that of the Phryganeidæ and suggests on embryological grounds the near relationship of the Thysanura to the Neuroptera.
So in a less degree does the head of the larvæ of certain Neuroptera and Coleoptera. The eyes are compound, the single facets forming a sort of heap. The clypeus and labrum, or upper lip, is, in all the Thysanura, carried far down on the under side of the head, the clypeus being almost obsolete in the Poduridæ, this being one of the most essential characters of that family.
It is homologous in situation with the middle pair of blades which composes the ovipositor of higher insects, and if it should prove to be used by the creature in laying its eggs, we should then have, with the spring, an additional point of resemblance to the Neuroptera and higher insects, and instead of this spring being an important differential character, separating the Thysanura from other insects, it binds them still closer, though still differing greatly in representing only a part of the ovipositor of the higher insects.
Thrush, pairing with a blackbird; colours and nidification of the. Thrushes, characters of young. Thug, remorse of a. Thumb, absence of, in Ateles and Hylobates. Thury, M., on the numerical proportion of male and female births among the Jews. Thylacinus, possession of the marsupial sac by the male. Thysanura. Tibia, dilated, of the male Crabro cribrarius.
After having studied the Thysanura enough to recognize the great difficulty of deciding as to their affinities and rank, the writer does not 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.
And it is a remarkable fact, as we have previously noticed, that when it begins to differ from the Caddis fly embryo, it begins to assume the Poduran characters, and its development consequently in some degree retrogrades, just as in the lice previous to hatching, as we have shown in a previous chapter, so that I think we are warranted at present in regarding the Thysanura, and especially the family of Podarids as degraded neuropters.
Diversified structures possessed by the males for seizing the females Differences between the sexes, of which the meaning is not understood Difference in size between the sexes Thysanura Diptera Hemiptera Homoptera, musical powers possessed by the males alone Orthoptera, musical instruments of the males, much diversified in structure; pugnacity; colours Neuroptera, sexual differences in colour Hymenoptera, pugnacity and odours Coleoptera, colours; furnished with great horns, apparently as an ornament; battles, stridulating organs generally common to both sexes.
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 example. In this he followed Latreille, who established the order in 1796. The Abbé Bourlet adopted the same view.
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