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by T. MARSHALL BELL, b.a., M.B., b.ch. 
Delivered before the Society on the 12th October, 1968 
In Genesis we are told how the SeFpent was condemned to "go upon the 
dust", and for what cause. It is implied that before God's curse he had limbs, but 
there is no mention of how he had acquired such appendages in the first place. 
However, before we can discuss the loss of limbs in vertebrate animals (namely 
Fishes. Amphibia. Reptiles. Birds and Mammals) we must first consider the 
origin of the two pairs of limbs which they mostly possess. 
Outside Russia, I think very few Biologists accept the views credited to the 
French biologist Lamarck, that living creatures acquire limbs or other characters, 
by striving after some action which requires them. Instead we believe that living 
matter has a continual tendency to mutate : that is, to develop changes which will 
be inherited by offspring, if those changes are not fatal to the animal or plant in 
which they appear. Whether mutations arise from an intrinsic instability of 
living matter, or are always caused by outside influences, such as radiation or 
chemical attack, is uncertain. But in whatever way the change may come, a 
mutated creature must do its best to suit its behaviour to its altered capabilities, 
and to make a livelihood helped or hindered by its mutation, or else it will 
perish and leave no descendants to carry on the mutated line. Development of 
limbs adds generally to the mobility of their possessor, but offers hostages to 
fortune when a predator seeks a protuberance to grab, and also hinders a body 
squirming through narrow gaps. Loss of limbs usually reduces mobility at first, 
though other mutations may compensate for this; but the loss aids burrowing 
and also hiding in crevices to escape enemies or surprise prey. It is perhaps 
significant that nearly all vertebrates that have lost their limbs are carnivorous. 
What we believe to be the most primitive relatives of vertebrates to be found 
today are the Lancelet, Amphioxus, and the larvae of Tunicates, Sea Squirts. 
These are not true vertebrates for they have no backbone; but they have a 
number of features allying them to the vertebrates. There are Gill-clefts in the 
Pharynx, that is the front part of the Gut. a structure called the Notochord, 
above the Gut. which serves as a primitive backbone, and a nerve cord above 
that again. So we must regard them as living survivors of the stem from which 
backboned animals arose. They have no paired limbs, nor any sign of ever having 
possessed and lost them. 
The next higher group, the Cyclostomes. whose best-known members are the 
Lampreys, are also limbless; and the pairs of fins or limbs characteristic of higher 
groups are found first only in the fossils of Fishes, which occur in beds laid 
down in the Devonian period. 
It seems likely, however, that there must have been an intermediate stage, in 
which a fish-like animal had a dorsal fin passing backward round the tail and 
dividing at the anus into lateral paired fin-folds, and (in most fish at least) into 
separate single dorsal and taii-fins. I must admit, though, that I have never 
heard of a fossil showing this structure, but remains of a primitive fish-like 
creature, called Jamoytius, found in Silurian shale, has been reconstructed by 
E. I. White to show a rather different development, in which the lateral fin-folds 
have no connexion with the single fin of the back and tail. 
The majority of typical fish have two pairs of fins, Pectoral and Pelvic, from 
which the paired fore- and hind-limbs of vertebrates appear to have developed. 
Many different lines of fish appear to have lost one or both pairs of fins and 
qualify for the popular designation of eels. Where only one pair of fins is lost, 
it appears an invariable rule that the hind or pelvic fins go and the fore or 
pectoral fin's remain. There may, however, be a catch here, because in some fish 
the origin from which the pelvic fins develop has moved so far forward as to be 
nearer the front of the animal than the pectoral fins. 
The Moray Eel. which lives in holes or crevices in rocks, has lost both 
pairs of fins. Part of its success is due to the compensating acquisition of a 
venomous bite. 
