Miscellaneous. 323 
We are thus led to conclude— 
1. That in the species above cited, which have their sexual gene- 
ration represented by gonophores always attached to the hydroid 
polype, or by semimedusee or free meduse, the ova originate in the 
interior of the hydroid polype itself, and not in these gonophores or 
meduse. 
2. That the ova are only differentiated cells of the endoderm, and 
that we can observe all the transitions between an ordinary endo- 
dermic cell and a well-developed ovum. 
3. That the ova are conveyed into a bud, which is at first only a 
diverticulum of the body-walls of the polype; that this bud en- 
larges, and finally becomes a gonophore, destined to be always 
attached, or a semimedusa or a free medusa. 
4. If we accept as demonstrated the facts that I have just ex- 
pounded, the gonophores, the semimedus, and the medusze cannot 
be regarded as sexual individuals ; consequently it would seem that 
alternation of generations cannot be accepted for these species.— 
Comptes Rendus, August 16, 1881, p. 345. 
Biological Evolution of the Aphis of the Alder * (Vacuna alni, 
Schrank). By M. J. LicwrenstErn. 
Among the Aphidians there exists a small group of insects which 
is distinguished from all the rest at the first glance by the mode of 
carrying the wings. Instead of being roof-like, as is the rule, these 
organs are laid flat upon the back, as in the males of the Coccide. 
Of these the Phyllowera is the best known type. I have already, 
some ten years ago, traced the evolutive cycle of this genus, show- 
ing the Phyllowera of the oak with two apterous and two winged 
forms, the Phyllowera of the vine with three apterous and a single 
winged form, and the Phyllowera acanthochermes, which is always 
apterous. 
Besides the genus Phyllowera, which has only three joints in the 
antennx, only two other genera carry their wings horizontally, 
namely Aplonewra, with six joints in the antennee, and Vacuwna, with 
five joints in the antenne. 
Only one species of Aploneuwra was known, namely the Aphis of 
the pistachio (A. lentisci) ; I discovered its sexual forms in a second 
on the roots of grasses. I regard this second species as a form of 
that of the pistachio, believing that there is a migration from the 
pistachio to the grasses, as also in that of the Phyllowera from the 
white oak to the green oak, and vice versd. 
It remained to study the Vacune, of which two species are known 
—V. dryophila on the oak and V. alni on the alder and birch. 
Vacuna dryophila lives on the green oak and the white oak ; 
and I have hitherto been unable to ascertain any regular migration ; 
but, at any rate, in December, a winged form appears under the 
leaves of the white oak (Quercus pubescens), and there deposits sexual 
- * There is also upon the alder another Aphis (Aphis aint of Kalten- 
bach, Koch, &c.) which is a true Apes with seven joints in the antenne, 
and has been placed by Passerini in the new genus PMerocallis. I only 
intend here to examine the Aphis with flat wings, allied to Phyllovera, 
with which it has even been sometimes confounded, 
