1893-94-] Exhibits in Natural History. 113 



drawing left off and begun again without trouble. The instrument is only 

 adapted for the lower and medium powers of the microscope. 



New Apochromatic 8-millimetre Objective. — This objective is one of Zeiss's, 

 and one of the most perfect glasses of its kind made. It has an aperture 

 of 80°. It is M'ell known that, with such an aperture and the necessary 

 low initial magnification, it has hitherto been most difficult with any or- 

 dinary microscopic objective to resolve P. angulatum into clots, — that is to 

 say, to show the hemispherical markings on this object. But this 8-milli- 

 metre glass does so perfectly, using a deep eyepiece, which its most perfect 

 achromatism allows one to use with it. When it first came into Mr For- 

 gan's possession, it was some time before he was able to use it at its best, 

 the reason, as it was subsequently proved, being that the microscope tube 

 was too long. AVhen the tube was reduced to 160 m.m. in length, the 

 definition became at once of the most perfect description. 



By Mr A. B. Steele. 



Pearls found in the Shells of the Common Mussel at Cramond. — These pearls 

 were found in specimens of the common mussel (Mytilus edulis) gathered 

 last summer on the shore at Cramond. Almost all the mussels contained 

 one small pearl, and some of them had more than one. In technical 

 language they are termed seed-pearls, and are interesting merely as curi- 

 osities. One or two, however, were about the size of a small pea, and had 

 the beautiful rose-tint of Scottish pearls, but unfortunately these were not 

 discovered until the mussels had been cooked. Although there is no in- 

 stance on record of a pearl of any value having been found in the common 

 mussel, yet, from the size and transparency of several of these pearls, there 

 is reason to think that gems of some commercial value may yet be found 

 in the Mytilus edulis. 



By Mr Coats. 



Chili Dragon-fly. — This dragon-fly (Phenes raptor) is said to be the largest 

 in Chili, and is 3| inches in length of body and 5 inches across the wings. 

 The specimen exhibited was a very fine one. 



By Mr Hugh Fraser. 



Spruce-fir Gall Aphis. — Specimens of the galls of the Fir Aphis {Chermes 

 Miixtis) were exhibited, attached to young twigs of the tree; and the 

 life-history of the insect was traced, from the gall to the imago or perfect 

 insect. It was explained that the only mode of destroying this insect 

 pest was to burn the infested twigs, when the gall made its appearance in 

 May. 



Fruiting Fig. — A Brown Turkey fig-plant, one year old, was exhibited 

 growing in a pot, and bearing eight well-formed figs. This precocity in 

 fruiting was attributed to the cutting having been taken from a well-ripened 

 shoot of an old fig. 



VOL. III. H 



