SCIENTIFIC SUMMARY. 
335 
aphides the preceding 1 summer, the eggs may he found, often still covered by 
the dried skin of the mother. The eggs are of a dull-yellow colour, and 
about ^ inch long. Early in the spring these eggs give birth to a little 
crawling insect which proceeds to attack the young tender leaves, on which 
it feeds, causing the leaf to pucker until it at last curls into a protective 
shelter for the so-called “ stem-mother.” After three months the latter 
begin to people the leaf with viviparously produced young at the rate of 
about one every six or seven hours. The second generation resemble their 
parent in many respects, but none grow so large ; they accumulate in 
immense numbers, and some of them, crawling away, form new colonies on 
other leaves. They produce the third generation, which is destined to 
acquire wings, and the individuals forming it, which are short-lived, deposit 
twelve or more “ pseudova ” at intervals of about half-an-hour. The young 
aphides, issuing from these, and constituting the fourth generation, are very 
active and move swiftly. They are of a brown colour, and in general 
appearance somewhat like those of the second generation. In this stage 
they swarm over every part of the tree, and their necessities often cause them 
to migrate, during which process great quantities of them are destroyed. 
The fifth generation is very similar to the fourth, but without wings. The 
aphides of the sixth generation all acquire wings. They abound in the latter 
end of June and the early part of July. They congregate on the bark, 
seeking out sheltered cracks and crevices in which they deposit their young, 
forming the seventh generation, which are sluggish and of the colour of the 
bark, the females being a little larger than the males. They have no mouth, 
but live motionless for a few days, during which the female seems to increase 
in size by the enlargement of her single egg. Both sexes soon perish, leaving 
among their shrivelled bodies the shining, brownish winter-egg from which 
this series of generations started ; so that, as Dr. Riley says, after a long 
series of vegetative (agamic) reproductions, at last the time comes for the 
renewing of the race by this zygospore-like body. — ( Journ . Roy. Micr. Soc ., 
June, 1879.) 
A Supposed Neiv Order of Crustacea. — In the February number of the 
American Naturalist , Dr. A. S. Packard, jun., observes that the Nebdliadce , 
represented by the existing genus Nebalia, have generally been considered 
to form a family of the Phvllopod Crustacea ; Metschnikoff, who studied the 
embryology of Nebalia, considering it to be a “ Phyllopodiform Decapod.” 
But besides the resemblance to the Decapods there is also a combination of 
Copepod and Phyllopod characteristics. The type, he points out, is an 
instance of a synthetic one, and is of high antiquity, having been ushered in 
during the earliest Silurian period, when there were (if we regard the 
relative size of most Crustacea, and especially of the living Nebalice) 
gigantic forms. Such was Dithyrocaris, which must have been over a foot 
long, the carapace being seven inches long. The modern Nebalia is small, 
about half-an-inch in length, with the body compressed, the carapace 
bivalved, as in Limnadia, one of the genuine Phyllopods. There is a large 
rostrum overhanging the head; stalked eyes, and besides two pairs of 
antennae and mouth-parts, eight pairs of leaf-like, short, respiratory feet, 
which are succeeded by swimming feet. There is no metamorphosis, 
development being direct. 
