28 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
The Group Vermidea. 
A RECENT number of Nature (August 24, 1916, 
p- 525) contains a notice of a work on Nematoda, 
which are described as *‘a group of Vermidea which 
presents great difficulties from a systematic point of 
view, and has therefore been less investigated than 
other groups of Vermidea.”” It may perhaps be asked 
what is the justification for this use of the term 
“ Vermidea.” 
In vol. v. (1897) of Delage and Hérouard’s well- 
known *Traité de Zoologie Concréte” it is pointed 
out (p. 1) that Schulgin and Pruvot had independently 
suggested the replacement of the denomination 
““Molluscoides"’ [=Brachiopoda+Polyzoa] by ‘ Ver- 
‘moides,”’ on the ground that the affinities of this group 
are with the worms rather than with the Mollusca. 
This idea appeared a happy one to Delage and 
Hérouard, who proposed to add to the group thus 
constituted certain small groups which they believed 
to have a real though distant affinity to the Polyzoa or 
to the Brachiopoda. The ‘groups thus added are the 
Gephyrea (Priapulida, Sipunculida, and Echiurida), 
the Axobranchia (Vermiformiz [=Phoronidea] and 
Pterobranchiz), and the Trochelmia (Rotiferia, Gas- 
trotrichiz, Kinorhynchia, and Chetognathia). These, 
with the Bryozoaria [=Polyzoa] and the Brachiopodia, 
constitute the enlarged embranchement, which now 
appears as the ‘‘ Vermidea.’’ On p. 327 it is stated 
that the Vermidea ‘sont liés entre eux par des 
affinités réelles’’; and the Platyhelminthes, the Nema- 
toda, and the Annelida are definitely excluded from 
this association. : 
Up to and including vol. xlii., for 1905, the Zoological 
Record included most of the groups of ‘* Worms” 
under the designation ‘‘Vermes.”’ In vol. xliii., the 
first which was issued as a volume of the International , 
Catalogue of Scientific Literature, ‘‘ Vermidea’’ re- 
places ‘‘Vermes,’’ and includes (1) Platyhelminthes, 
Nemertinea, Mesozoa; (2) Nemathelminthes; (3) 
Cheetognatha, Rotifera, Gastrotricha; (4) Archian- 
nelida, Polychaeta, Oligocheta, Gephyrea, Phoro- 
nis, and Hirudinea; and to these may be added Ptero- 
branchiata, which appears in the Contents, p. xii., 
though not in the formal list given at the beginning 
of the detailed account of the literature of these forms. 
I am not aware what was the authority for this use 
of *“ Vermidea”’; but it may be noted that it omits the 
Polyzoa and the Brachiopoda, the two central groups of 
Delage and Hérouard’s phylum; and that it includes 
the Platyhelminthes, Nemathelminthes, and Annelida, 
three groups which were expressly excluded by those 
authors. The group.“ Vermidea” of the Zoological 
Record is thus absolutely different from that of the 
“Traité de Zoologie Concréte.” Not only does the 
propriety of so revolutionary a change seem question- 
able, but one may well ask in what way was the new 
departure an improvement on the old group ‘‘ Vermes,” 
which was admittedly an assemblage of forms which 
have no demonstrable affinity to one another. It is 
not possible to say much more for the grouping than 
that the majority of forms thus associated are inverte- 
brates having a shape suggested by the term ‘ worm,” 
or, in other words, that they are longer than they 
are broad. 1 
NO. .2446, VoL. 98] 
NATURE 
‘another. 
[SEPTEMBER 14, 1916 
I do not desire to discuss the validity of Delage and 
Hérouard’s phylum, although I am by no means con- 
vinced that the groups included in it are allied to one 
But in the sense in which it was defined in 
1897 it indicated an attempt to advance the classifica- 
tion of animals. The procedure adopted by the 
Zoological Record appears to me to have nothing to 
recommend it. There is no doubt some convenience, 
from the point of view of the recorder, in dividing 
the animal kingdom into a small number of com- 
prehensive groups. If the forms under consideration 
were described as ‘‘ worms" it would be an admission 
that the name of the group was adopted merely for 
motives of convenience. The term “‘ Vermes”’ was no 
doubt rightly rejected, since most zoologists would — 
agree that it has no more claim to a permanent place 
in literature than has *‘ Radiata,” another assemblage 
which included animals possessing a type of symmetry 
which in itself is not now regarded as necessarily 
indicating affinity to other animals similarly provided. 
The use of “‘ Vermidea” in the sense of the Zoological 
Record can only be described as pseudo-scientific. It 
is not only no improvement on “ Vermes,”’ but its sub- 
stitution for that term is misleading, as suggesting 
that it is a more natural group than the one which 
it replaced, Srpney F. Harmer. ~ 
British Museum (Natural History) 
August 27. : 
‘ 
The Refractometry of Lenses. 
Ir may be of value to opticians and others to know 
of a method by which the refractive indices of irregular 
or unpolished pieces of glass, lenses, or prisms, can 
be found fairly accurately—i.e. to 1 in the fourth 
decimal place. ave 
The specimen is immersed in a mixture of carbon 
disulphide and alcohol contained in a prism cell having 
refracting sides of. optically plane glass; this cell is — 
used on the table of a spectrometer. : 
By altering the proportions of the two liquids, the 
refractive index of the mixture can be made equal to 
that of most specimens. This is easily done by ob- 
serving the image of the slit refracted through the 
system. The finest adjustment of proportion takes — 
place automatically through unequal evaporation. —_ 
The important ‘prevision is that the liquid must be 
mechanically stirred;. this can be done by a small 
‘““propellor’’ blade driven by a motor, which must be 
quite separate from the spectrometer to obviate vibra- 
tion. : * 
At the proper moment the angle of minimum devia- 
tion is taken, and the refractive index calculated out 
in the usual way. ; 
The method has given excellent results for refractive 
index and dispersion on a number of varying speci- 
mens. It should prove of use for copying optical 
systems. The method is at present being developed, 
and full details will be published shortly. 
__L. C. Martin? 
Imperial College of Science and Technology, 
South Kensington, London, S.W., August 23. 
An Oil Drive for Equatorial Telescopes. 
Tue drive, or oil, regulator under consideration is 
the invention of Mr. G. H. Denison, of Hunslet 
Foundry, Leeds, past president of the Leeds Astrono- 
mical Society. The device has been attached to the 
pedestal which carries the 26-in. reflector, and is fitted 
on the south side opposite the driving clock. 
With the help of the accompanying photograph, the 
working of the device may be briefly described as 
follows :— ; 
—— a 
