to bud out several generations more, by internal gemmation, as long as the warm weather lasts.  According to M. Lichtenstein, all previous observations have been made only on aphides of this third type; and he maintains that every species in the whole family really undergoes an analogous alternation of generations.  At last, when the cold weather begins to set in, a fourth larval form appears, which soon obtains wings, and flies back to the same kind of oak on which the foundresses were first hatched out, all the intervening generations having passed their lives in sucking the juices of the other oak to which the second larval form migrated.  The fourth type here produce perfect male and female insects, which are wingless, and have no sucking apparatus.  The females, after being impregnated, lay a single egg each, which they hide in the bark, where it remains during the winter, till in spring it once more hatches out into a foundress, and the whole cycle begins over again.  Whether all the aphides do or do not pass through corresponding stages is not yet quite certain.  But Kentish farmers believe that the hop-fly migrates to hop-bines from plum-trees in the neighbourhood; and M. Lichtenstein considers that such migrations from one plant to another are quite normal in the family.  We know, indeed, that many great plagues of our crops are thus propagated, sometimes among closely related plants, but sometimes also among the most widely separated species.  For example, turnip-fly (which is not an aphis, but a small beetle) always begins its ravages (as Miss Ormerod has abundantly shown) upon a plot of charlock, and then spreads from patches of that weed to the neighbouring turnips, which are slightly diverse members of the same genus.  But, on the other hand, it has long been well known that rust in wheat is specially connected with the presence of the barberry bush; and it has recently been proved that the fungus which produces the disease passes its early stages on the barberry leaves, and only migrates in later generations to the growing wheat.  This last case brings even more prominently into light than ever the essential resemblance of the aphides to plant-parasites.

THE MILK IN THE COCO-NUT

For many centuries the occult problem how to account for the milk in the coco-nut has awakened the profoundest interest alike of ingenuous infancy and of maturer scientific age.  Though it cannot be truthfully affirmed of it, as of the cosmogony or creation of the world, in the ‘Vicar of Wakefield,’ that it ‘has puzzled the philosophers of all ages’ (for Sanchoniathon was certainly ignorant of the very existence of that delicious juice, and Manetho doubtless went to his grave without ever having tasted it fresh from the nut under a tropical verandah), yet it may be safely asserted that for the last three hundred years the philosopher who has not at some time or other of his life meditated upon that abstruse question is unworthy of such an exalted name.  The cosmogony and the milk in the coco-nut are, however, a great deal closer together in thought than Sanchoniathon or Manetho, or the rogue who quoted them so glibly, is ever at all likely, in his wildest moments, to have imagined.