The President's Address. 
73 
the varied forms observed are referred. The existence of 
twin crystals^ and the not nnfrequent occurrence of a ^' half 
crystal are satisfactorily established, and we are taught how 
many of the apparently aberrant forms may be explained by 
considering them as phases of the half crystal ; the existence 
of crystals other than octohedra is also distinctly announced. 
All that relates to the characters of arsenious acid is of high 
interest from the grave questions which are frequently in- 
volved in medico-legal investigations of which it is the 
subject. Regarded from this point of view, I think this com- 
munication fairly deserves to be considered the most impor- 
tant and most interesting of the many interesting papers of 
the year. You all, I am sure, have much satisfaction at now 
being able to reckon its learned author among the members 
of the Microscopical Society. The author assures us that one 
of his objects in presenting this paper was to show "by a 
striking instance the great value of the binocular microscope 
as a means of diagnosis,^^ and in summing up the results of 
his inquiries, gives important testimony to its usefulness. He 
remarks : — " I felt that my views concerning the large part 
played by the half crystal, though highly probable, were still 
only probable ; but under the binocular microscope all my 
doubts were dissipated, my errors corrected, some surmises 
confirmed, and most of my inferences justified.^^ He adds : — 
" If there is any one who doubts the vahie of this form of 
microscope, or is disposed to treat it simply as a philosophical 
toy, I would ask him to examine these crystals with the 
monocular instrument by transmitted light, and with the 
binocular instrument by reflected light — "the fine relief 
and perfect roundness of the tube and its contents is at one 
and the same time a proof of the utility and faithfulness of 
the binocular microscope." 
c. On Zoology. 
1. "On the Circulation in the Tadpole," by W. U. Whitney, 
Esq. (Read June 13th, 1861. ' Tr. Mic. Soc. Lond.,' n. s., 
vol. X, p. 1). 
In this paper we have additional testimony to the value of 
the binocular microscope, applied to investigations in a widely 
diflPerent field of research. 
2. " On the Metamorphoses of a Coccus found upon 
Oranges," by Richard Beck. (Read March 13th, 1861 . ' Tr. 
Mic. Soc. Lond.^ n. s., vol. ix, p. 47). 
The author describes the development of a species of coccus 
found under the shield commonly met with on the sweet or- 
anges sold in the shops ; they are not so common on the fruit 
sold in the streets. To those who propose to take advantage 
