THE MEDITERRANEAN NATURALIST 
425 
Geomalacns (Let.) Tournieri Poll. 
G. Tournieri Poll., Rec. Arion., Boll. Mas. Toino, 
1890, N° 17, p. 38. 
Hab. Contorni di Oran (Tournier). 
G-eomalacus (Let.) arlanticus Bgt. 
Letoourneuxia atlantica Bgt. in Pechaud, Excars. 
Mai. N.Afr., 1883, pag.G. 
G. atlanticusVoM ., Rec. Arion., Boll. Mas. Torino, 
1890, N° 87, p. 38. 
Hab. Presso le Cascade del Safsaf presso Tlerncen 
(Pech.). 
II Bourgnignat (Male. Alg., p. 33) cita ancora, 
sulla testimonianza di Aucapitaine, V Arion rufus 
dell’interna dell’Algeria, rna siccome nfequesta, ne 
alcun’altra specie del genere Arion fa mai pin ri- 
trovata in tali region!, cosi e assai probabile che il 
supposto A. rufus sia an Geomalacus. 
Method of taking Plaster Oasts of objects 
of Natural History. 
At a recent meeting of the Manchester Micros- 
copical Society Professor Boyd Dawkins F.R.S., 
exhibited a number of casts in plaster of Paris 
of various objects of natural history, and explained 
the process by which anyone can make them for 
himself, The material of the mould is artistic mo- 
delling wax, which is a composition akin to that 
which is. used by dentists. And as it becomes soft 
and plastic by the application of heat, though in 
a cold state it is perfectly rigid, it may be applied 
to the most delicate object without injury. As it 
takes the most minute markings and striations of 
the original to which it is applied, the microscopic 
structure of the surface is faithfully reproduced in 
the cast. The method is briefly this: — 
1. Cover the object to be cast with a thin powder 
of steatite or French chalk, which prevents the 
adhesion of the wax. 
2. After the wax has become soft, either from 
immersion in warm water or from exposure to the 
direct heat of the fire, apply it to the original, be- 
ing careful to press it into the little cavities. Then 
carefully cut off the edges of the wax all round, 
if Che under cutting of the object necessitates 
the mould being in two or more pieces, and let 
the wax cool with the object in it, until it be suf- 
ficiently hard to bear the repetition of the opera- 
tion on the uncovered portion of the object. The 
steatite prevents the one piece of the mould stick- 
ing to the other. The original ought to be ta- 
ken out of the mould before the latter becomes 
perfectly cold and rigid, as in that case it is very 
difficult to extract. 
3. Then pour in plaster of Paris, after having 
wetted the moulds to prevent bubbles of air lurk- 
ing in the small interstices, and if the mould be 
in two pieces, it is generally convenient to fill them 
with plaster separately before putting them toge- 
ther. 
4. Then dry the plaster casts either wholly or 
partially. 
5. Paint the casts in water colours which must 
be fainter than those of the original, because the 
next process adds to their intensity. The delicate 
shades of colour in the original will be marked in 
the cast by the different quantities of the same co- 
Lmr which are taken up by the different textures 
of the cast. 
6. After drying the cast steep it in hard paraffin. 
The ordinary paraffin candles, which can be ob- 
taind from any grocer, will serve the purpose. 
7. Cool, and polish the .cast by hand with stea- 
tite. 
The result of this process is far better than that 
obtained by any other. The whole operation is 
very simple, and promises to afford a means of 
comparison of natural history specimens in differ- 
ent countries which has long been felt to be a 
scientific need. Casts of type specimens may be 
multiplied to any extent at a small cost of time and 
money, and are as good as the original for purposes 
of comparison, and almost as hard as any fossil. 
Professor Boyd Dawkins has employed it for 
copying ffint implements, fossils, and bones and 
teeth which can scarcely be distinguished from the 
originals. 
The Orange Disease in Cape Colony. 
Ceratitis citriperda — (Ll/ac Leay). 
By S. D. Bairstow, F. L. S. 
(Continued). 
Along with Dr. Chute I made a careful exa- 
mination of the legless maggot under a high 
power, 
