218 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 
Lima hians and its Mode of Life. 
By J. D. F. Gitenrist, M.A., B.Sc. Ph.D. 
[Read 29th January, 1895. ] 
Ir seems to be a general rule in the Animal Kingdom that with 
the cessation of the struggle for existence there is a degeneration 
of the organism ; in other words, in proportion to the ease with 
which an animal finds its food and its security against enemies is 
the decrease in the complexity of its organisation. This law 
‘could not be illustrated more forcibly (excluding parasitic life) 
than in the group of the Bivalve Mollusca, Nothing is simpler or 
easier than their mode of procuring nourishment. The animal is 
enclosed between two shells, and the food consists of the particles 
of organic matter (diatoms, protozoa, larve, ce.) sifted out from the 
current of water created by the ciliated gills and passing between 
the shells. The animal, moreover, is usually so securely protected 
by its thick calcareous shells that comparatively few enemies in 
proportion to its numbers and varieties care to tackle so formidable 
a mouthful. We may instance as a typical example the common 
Oyster, belonging to the group with which we are here concerned. 
In such cases degeneration begins in the most highly developed 
and most unstable part of the organism, viz., the nervous system 
and its associated sensory organs. As these are chiefly located 
in the head region, this is the first part to exhibit traces of the 
retrograde process, In the Bivalves this has proceeded so far 
that the head has entirely disappeared. In the case of the Oyster, 
degeneration has gone even further, and there is, in addition, the 
loss of the foot or organ of locomotion, so that the whole activity 
of the creature is reduced almost to the lowest vegetative existence. 
Simple as is this mode of life, however, many points regarding 
food supply, growth, and propagation, of importance from a 
scientific as well as from an economic point of view, require 
renewed and scientific investigation. 
The Oyster finds an effective, if. sole, mode of protection in its 
huge shells. The only call upon the organism in the way of 
defence seems to be the adding to these of additional layers of 
carbonate of lime, 
a 
