1868. | Zoology. 591 
of which he satisfactorily accounts by the isolation of the respective 
parents. If, he says, we regard the species of a genus as descendants 
of a common primitive form, and at the same time, in accordance 
with the well-known experience of gardeners, regard their various 
peculiarities as so much better fixed, or so much less variable, the 
earlier they were acquired, the longer they have been inherited 
unchanged, it becomes intelligible that, above all, the characters 
proper to the primitive form persist; and consequently in the crossing 
of two species, these are more readily transferred to the hybrid than 
later-acquired peculiarities of the father or mother. From this 
point of view, Dr. Miller thinks we shall be able to explain many 
peculiarities of hybrids and, vice versd, perhaps in many cases to 
trace from the form of the hybrids to the primitive form of the 
genus ; the latter of course only with the greatest care, for the mere 
fact that the hybrids produced by males of one species with females 
of another, do not agree with those produced by males of the second 
species with females of the first, furnishes a proof that other cir- 
cumstances aid in determining the form of the hybrids. 
The Ancestry of Insects.—Dr. Anton Dohrn, of Jena, has lately 
described a new fossil insect, which he calls Hugereon Baeckingi, 
and which leads him to make some observations on the development 
of Insects by Natural selection. This Eugereon has characters 
intermediate between those of the Hemiptera and Neuroptera, and 
must, says Dr. Dohrn, be regarded as genetically related to the two 
orders. He does not think, however, that it was the common 
ancestor of these two groups, for the Neuroptera are found along 
side of it, but he believes that at a period not much earlier an insect 
form existed completely intermediate between the Neuroptera and 
Hemiptera, from which these two orders were differentiated and from 
which EHugereon also was descended, not having become so much 
modified. Dr. Dohrn then tells us of Haeckel’s views (also a Jena 
professor) whose book we spoke of as most significant when it first 
appeared. Haeckel says that Insects, Spiders, Centipedes, and Crus- 
tacea must have had a common ancestor. The ancestral form of the 
Crustacea is known, appearing in their development as the Zoée. 
The ancient adult Zoéz or Zoepoda, as Haeckel calls them, flourished 
early in the Silurian period according to that author, and it was 
probably about the Devonian epoch that certain Zoepods were 
naturally selected for a terrestrial life, developed trachez and became 
Protracheata, or progenitors of all the great Tracheiferous group of 
the articulate-limbed animals; whilst those which remained in the 
water are the ancestors of the Branchiferous forms called crabs, 
lobsters, and shrimps. Whether any Protracheata still exist is, 
says Haeckel, doubtful: perhaps the Solifuge, a strange group of 
aberrant spiders, and also those insects which have no wings (not 
through disuse as in many cases, but by their progenitors never 
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