of Edinburgh, Session 1881-82. 
581 
structures. Moreover, there is really nothing which would make it 
unlikely on a priori grounds that this interpretation is the right one. 
M. Joliet has recently come to the conclusion that the so-called 
ganglion of Melicerta * is not a ganglion at all, but a gland. What 
the nature and homologies of this gland may be, is a question which 
can only he decided by a careful study of other Mollusca and of its 
development ; several views as to its nature obviously suggest them- 
selves, but in the absence of any more comprehensive information 
than is contained in this paper, it would be mere waste of time to 
consider any of them. 
Plate I. 
Fig. 1. Transverse section through nerve collar of Lymnseus, x 20. 
Fig. 2. Transverse section through nerve collar of Planorbis, x 20. 
Fig. 3. Transverse section through cerebral ganglia of Planorbis, 
showing glandular mass (a) lying above commis- 
sure, x 120. 
Fig. 4. Transverse section through one cerebral ganglion of 
Lymnseus, showing glandular mass (a) lying above 
commissure, x 120. 
Fig. 5. Cerebral ganglion of Lymnseus, showing commissure ( b ) 
which unites it to its fellow, and glandular mass 
(a), x 20. 
Fig. 6. Transverse section through pedal ganglion of Planorbis 
(a), is the unpaired small medium ganglion, x 75. 
Fig. 7. Single “ acinus ” from glandular mass of Planorbis, x 300. 
Fig. 8. Nerve cell (a) from cerebral ganglion of Lymnseus and 
“ gland cells ” (b), x 300. 
4. A Critical Examination of two cases of unusual Atmo- 
spheric Kefraction described by Professor Yince. By 
Edward Sang, C.E. 
The two phenomena, the subjects of the present paper, have 
found a place in the current popular scientific literature of the day, 
and exercise a considerable influence on the opinions of the casual 
votaries of science, and even of some of those who are its regular 
cultivators. For that reason I shall go more into detail than other- 
wise would have been needed. 
* Comptes Hendus, Nov. 7, 1881. 
