576 
Proceedings of the Boyal Society 
2. Observations on Vegetable and Animal Cells; their Struc- 
ture, Division, and History. Part I., The Vegetable Cell. 
By J. M. Macfarlane, B.Sc. Communicated by Professor 
A. Dickson. 
3. On some Points in the Anatomy of the Nervous System of 
the Pond Snails, Planorbis and Lymnseus. By P. E. 
Beddard, B.A., New College, Oxon. Communicated by 
Mr P. Geddes. 
The best figures of the nervous system of these animals are those 
of Lacaze-Duthiers, - in his Paper Sur les Otocystes des Mollusques , 
and in that Sur le Systeme Nerveux des Gasterojpodes * By a care- 
ful study of the nervous system of these two gasteropods, chiefly by 
cutting sections, I have discovered one or two small points in their 
anatomy which, as far as I can make out, have hitherto escaped 
attention. 
These two types, though so closely allied, differ to a considerable 
extent in the arrangement and structure of certain of their ganglia ; 
compare the figures given by Lacaze-Duthiers of the nervous system 
of Lymnseus on Plate xvii. in Volume i. of his Archives with that 
of Planorbis on Plate iii. of the same volume. It will be seen at 
once that the cerebral ganglion of Lymnseus is far more complicated 
than that of Planorbis, consisting of five separate lobes, while that 
of Planorbis appears to be made up of not more than two. 
Otherwise, the number of ganglia in the two is the same, but the 
asymmetry is different, the larger parietosplanchnic ganglia being on 
the right side in Lymnseus and on the left in Planorbis. 
By cutting several series of sections of the whole nervous 
system of Planorbis and Lymnseus, and arranging them carefully in 
order, one or two more points of difference in structure have been 
noticed. In fig. 1, which represents a complete section taken 
through the nerve collar of Lymnseus at the level of the pedal 
ganglia, it will be seen that these ganglia are united by a double 
commissure, the lower of the two commissures is much slighter than 
the upper, and was far more difficult to find ; the upper stouter 
* Archives de Zool. Exyerim. ct Generate, vol. i. 1872. 
