SCIENTIFIC SUMMARY. 
381 
M. Perrier very justly asks what can "be the usual food of an animal with 
such a digestive cavity. The dorsal skeleton is, however, represented by 
scattered perforated calcareous plates, each bearing a small spine. Through 
the membrane the circular canal surrounding the mouth, and the ambulacral 
vessels starting from it, may be recognized, but no caecal prolongations of the 
stomach into the arms were to be detected. The arms possess a double 
row of ambulacral tubes, but no genital glands could be discerned in them. 
The skeleton of the arms consists of four rows of pieces, two of which form 
a dorsal ridge, and partially cover the others, which are placed on each 
side, and each of which bears a median spine enclosed in a soft sheath, 
clavate, and bearing at the apex a tuft of pedicellariae, the latter being of 
the kind denominated ‘ pedicellaires croises’ by M. Perrier, and peculiarly 
characteristic of the Asteriadae, the most typical group of the true Star- 
fishes. The lateral plates form the borders of the ambulacral groove, in 
which the ambulacral vessel rests exactly as in the Comatulce , there being 
no ambulacral plates, such as occur in all known Stellerida. M. Perrier 
remarks, that the contrast between the arms and the disc, the probable 
absence of genital glands from the arms, and the absence of stomachal 
coeca, would seem to approximate this form to the Ophiurida, just as the 
structure of the arms would ally it to the Comatulae; but although in 
the abnormal characters above cited, and especially the want of ambulacral 
and buccal plates, it differs from all known Stellerida, the evidence of the 
pedicellariae leads him to class it in that group, as forming an aberrant 
family of the Asteriadae, in the neighbourhood of the genera Labidiaster , 
Pedicellaster, and Brisinga, which also possesses only two rows of ambulacral 
tubes. M. Perrier names this singular Starfish Hymenodiscus Agassizii. It 
was obtained within sight of the island of Dominica, from depths of 321 
and 450 fathoms. — Comptes Rendus, 30th August, 1880. 
Reproduction of Aphides.— M. Jules Lichtenstein has summed up the 
results of his observations upon the reproduction of the Aphides in a paper 
communicated to the French Association for the Advancement of Science. 
Starting from the principle that the biological cycle of an insect, com- 
mencing from the egg laid by a fertilized female, is not complete until we 
arrive at the same form of female fitted for fertilization, M. Lichtenstein 
regards all the different stages which succeed one another between these two 
extremes only as intermediate larval forms. 
His first experiments were made on the phylloxera of the oak (P. quercus). 
The egg attached to the bark of Quercus coccifera gives origin at the end of 
April to an apterous form, which he names the Founder. It moults four 
times, and then produces egg-like bodies, which it sticks to the petiole and 
lower surface of the leaves. These bodies are not true eggs, and their pro- 
ducer is called not a female, but a Pseudogyne , by M. Lichtenstein. From the 
pseudovum proceeds the first larval form (the Pseudogyne fondatrice), 
which is apterous and larger than any of the succeeding forms. From its 
gemmations issues the second larval form, which, after four moults, 
acquires wings, but is still only a pseudogyne. It quits the Quercus 
coccifera about May 20, and settles under the leaves of Quercus pubescens. 
This is M. Lichtenstein’s Pseudogyne emigrante. 
In its new abode this second form acts like the first, depositing oviform 
