APRIL 29, 1897 ] 
NATURE 
607 
imagine that the ions work their way through the solution by a 
‘continual series of interchanges between the parts of two 
solute molecules when in collision. The frequency of collision, } 
and therefore the ionic velocity, would then vary as the square 
of the concentration, so that the conductivity would depend on 
the cube of the concentration. 
(3) The potential difference at the contact of two solu- 
tions of different concentrations has the value calculated on 
the assumption that the ions migrate independently of each 
other, so that the faster-travelling ion enters the neighbouring 
solution first, and gives it a charge which continually increases 
till the electrostatic forces prevent further separation. 
It is such phenomena as these, and not the numerical relations 
between conductivity and osmotic pressure effects, which seem 
to me to offer the most convincing evidence in favour of the 
dissociation theory. W. C. DAMPIER WHETHAM. 
Trinity College, Cambridge, April 24. 
Mosquito-Bites. 
AN acquired immunity from the bites of mosquitoes and 
** domestic pests” is not uncommon in British India, and I have 
rejoiced in it myself, but should not trespass on you for space 
for details. I can give them to any of your correspondents who 
may care to ask me. 
There is lying before me a queer old case of mosquito-bite 
reported by a good witness, Pedro Teixeira, who sailed from 
Malacca to Mexico in 1600 A.bD., and crossed the latter from 
Acapulco to San Juan de Ulua, on his way to Spain. Of this 
journey he says: ‘* Almost all along this road is a plague of 
mosquitoes, so terrible and grievous that no defence avails against 
them, avd they stung my best slave to death.” 
102 Cheyne Walk, Chelsea, April 9. W. F. SINCLAIR. 
THE NATURAL AISTORY OF WORMS? 
HIS is the third volume that has been issued of 
“The Cambridge Natural History.” The previous 
volumes are vol. iii., Molluscs and Brachiopods (re- 
viewed in NATURE, lii. p. 149), and vol. v., Peripatus, 
Myriapods, and Insects (reviewed in NATURE, lil. p. 
322). In the multitude of the divisions in the animal 
kingdom with which it deals, the present volume differs 
considerably from its predecessors. It is true that one 
may even nowadays find most, if not all, of the many 
forms of life here described included in one hetero- 
geneous section entitled Vermes ; but the editors of the 
present book fully recognise the great distinction that 
exists between such forms as the Platyhelminthes or 
flatworms, the Oligochzta or earth-worms, the Rotifera, 
and the Polyzoa, and they have very wisely distributed 
the various sections to authorities whom every one will 
recognise as among the most competent to deal with 
their respective subjects. Indeed it may be questioned 
whether the separation of the subjects has not been 
carried a little bit too far. It is true that pages ix. to 
xil. contain what purports to be the scheme of classi- 
fication adopted in the volume, but this is little more 
than a table of contents, in which no attempt is made to 
show the relationships of the orders or families men- 
tioned ; and, apart from this, the only bond of union 
between the various sections appears to be the quotation, 
very happily adapted from André de Chénier, “ Nous 
allons faire des vers ensemble.” We should much like 
to have seen some attempt on the parts of the editors to 
present their readers, all of whom are not supposed to 
be familiar with the newest ideas of zoology, with a short 
introduction showing how and why it is that this “old 
group of Vermes” has gradually been dismembered, so 
1“ The Cambridge Natural History.”’ Vol. IT. : Flatworms and Mesozoa, 
by F. W. Gamble ; Nemertines, by Miss L. Sheldon ; Thread-worms and 
Sagitta, by A. E. Shipley; Rotifers, by Marcus Hartog; Polychaet 
Worms, by W. Blaxland Benham; Earthworms and Leeches, by F. E. 
Beddard ; Gephyrea and Phoronis, by A. E. Shipley ; Polyzoa, by S. F. 
Harmer. The whole edited by S. F. Harmer and A. E, Shipley. 8vo. 
Pp xii. + 560; with numerous illustrationsin the text. (London: Macmillan 
and Co., Ltd., 1396.) 
NO. 1435, VOL. 55] 
that now we find not only such forms as the Platy- 
helminthes and the Polyzoa claiming to rank as inde- 
pendent phyla of the animal kingdom, but we also find, 
in the scheme of classification at all events, the genus 
Phoronis, the few forms composing the Dicyemide and 
Orthonectida, and the thirty or so genera of leeches 
placed on the same high level. When we are told, as 
box. 
y <Y)\y, 
CY--- <W\ \ 
SS Jee 
fl Z 
Ce Ope, 4 . ZZ== 
& 
fA 
EF 
of 
in 
LL ELIT 
ge 
Fic. 1.—Diagrammatic view of the structure of Planaria lactea, a Turbel- 
larian. 7. The body has been cut across and a portion removed. 
Mr. Gamble tells us, that the Turbellaria “ occupy the 
lowest position in the whole group of worms,” that they 
“are most closely allied to that great extinct group from 
which they, the Nemertinea, Rotifera, and even the 
Annelids, offer increasingly convincing evidence of 
having been derived,” then we ask, What are we to 
