UARY 27, 1923] 









































Letters to the Editor. 
he Editor does not hold himself responsible for 
| opinions expressed by his correspondents. Neither 
can he undertake to return, nor to correspond with 
the writers of, rejected manuscripts intended for 
_ this or any other part of NatuRk&. No notice is 
taken of anonymous communications. | 
: Palzontology and Archaic Fishes. 
Tr is now a apr many years since I first decided 
to devote myself to the study of vertebrate morpho- 
logy. I was attracted to this study through feeling 
in the old days at Cambridge that the position of 
ative neglect into which this science had 
was the fault, not of the subject itself, but 
ther of that band of enthusiasts who, carried away 
the inspiration of Darwin, and setting to work 
the building of the new morphology, took in their 
te but little heed that the foundations upon which 
they built were adequate either in extent or in sound 
workmanship. As regards the former, an important 
in the Syandations was glaringly visible in the 
Tegion occupied by these two exceedingly archaic 
subdivisions of the Vertebrata—the Crossopterygii 
nd the Dipnoi. In particular, nothing whatever 
was known regarding the early developmental stages 
of any crossopterygian or of either of the two lung- 
fish which seemed nearest to the evolutionary stem 
of the terrestrial vertebrates. It was the recognition 
of the importance of this gap in the foundations of 
vertebrate morphology that, above all, influenced 
‘me in taking the decision to do what I could towards 
making the gap less extensive. Seeing that so much 
of my research work has been concerned with the 
two groups I have indicated, I may perhaps be 
arded as justified in having a special interest in 
n and their relation to the general problems of 
ebrate morphology. 
I am in consequence particularly interested to find 
the newly published Proceedings of the Linnean 
Soci the presidential address of Dr. Smith 
Woodward entitled ‘‘ Observations on Crossopterygian 
and Arthrodiran Fishes.”’ In view of the iremdent’s 
‘position as the official head of British paleontology, 
and still more in view of his pre-eminent position as an 
investigator of the paleontology of the lower verte- 
brates, his words will carry great weight where he 
is dealing with paleontological fact. In the course 
of his address, however, he comes into touch with some 
the broader questions of vertebrate morphology, 
p answers to which, if they are to be trustworthy, 
ist necessarily be based upon the judicial con- 
 Sideration of all the evidence available, and not 
‘merely of that which is constituted by the data 
regarding skeletal structure afforded by paleontology. 
It is, I think, particularly necessary to remind the 
younger generation of workers, to whom will fall 
e task of restoring morphology to its proper 
Position in biological science, that as regards several 
of the questions dealt with by Dr. Smith Woodward, 
due heed must be given to witnesses other than 
- It would not, for example, be gathered from the 
address in question that we do not all accept Dollo’s 
view that the modern lung-fish have ‘‘ abandoned 
the fusiform shape which is adapted for free-swimming 
life, and have become (secondarily) more or less 
eel-shaped in adaptation to a wriggling and grovelling 
- existence.”’ 
compa 
tallen 
_ There is no general characteristic of the Vertebrata 
more fundamental than the fact that during early 
_ Stages in their development their muscular system 
consists of segmentally arranged blocks of longi- 
NO. 2778, VoL. I11] 
NATURE 
113 
tudinally-running fibres along each side of the body. 
There is no — from the physiological implication 
that this peculiar arrangement of the muscular 
system has for its function the production of move- 
ments of lateral flexure. To some of us, the further 
conclusion appears to be equally inevitable that the 
vertebrates in general were in early stages of their 
evolution ‘‘ more or less eel-shaped in adaptation to 
a wriggling and grovelling existence.” 
The view may of course be held that, even ad- 
mitting that the primitive vertebrates were elongated 
in form, yet the ancestors of existing Dipnoi were, 
for a time during their evolutionary history, fusiform 
—just as was undoubtedly the case with the ancestors 
of the eel-shaped teleostean fishes. 
Whichever view is taken as to the fusiform 
ancestral stage of the Dipnoi—whether primitive 
or merely intercalated—I regard the evidence in the 
way of known facts as quite inadequate to form the 
basis of any such idea. This evidence is palxonto- 
logical in its nature, Stated shortly and crudely, 
it is constituted by the fact that the palaozoic 
dipnoans with which we are acquainted up to the 
present are on the whole fusiform, while the modern 
dipnoans are elongated in form. 
ersonally, I take the view that the vertebrates, 
during the prolonged early phases of their evolutionary 
history before they evolved into creatures highly 
specialised, on one hand, for a purely swimming 
habit—like the modern fish—or, on the other, for 
a terrestrial existence as are the modern tetrapods, 
were actually, in all probability, creatures of elongated 
form of body which “ wriggled and grovelled "’ in a 
swampy environment. Further, I believe that such 
conditions are highly unfavourable (1) to existence in 
crowds or shoals, and (2) to that rapid enclosure in 
preservative silt or other deposit which is essential to 
their persistence as fossils. Consequently I should 
attach very little weight to the fact that the specimens 
known to us as fossils of the paleozoic dipnoans 
happen to have fusiform bodies. As a matter of 
fact, I regard the fusiform body just as I regard 
the divided-up median fin and the heterocercal tail 
(or its further development the homocercal tail), as 
marks of the efficient swimmer. They are character- 
istics which I should expect to find in the majority 
of species in any group of fish during its period of 
maximum prosperity, when it reached the highest 
degree of adaptation to a purely swimming existence. 
Dr. Smith Woodward mentions the failure up to 
the present to discover fossil links between the paired 
fin of the crossopterygian and the leg of the terrestrial 
vertebrate. I suppose I am still in the position of 
being the only investigator of the evolutionary 
history of the vertebrate limb who has had at his 
disposal embryological material of Polypterus and 
of all the three genera of lung-fish in addition to 
that of elasmobranchs and amphibians. It may be 
well, then, to state that my own work, together with a 
careful consideration of the work of others, palzonto- 
logists, anatomists, and embryologists, leaves no 
doubt in my mind that the reasonable view to take 
is that which regards the paired fin (of whatever 
type—archipterygial, crossopterygial, or actino- 
pterygial) on one hand, and the pentadactyle leg 
on the other, as being limbs specialised for different 
types of movement, neither of which has evolved 
out of the other, but each of which has evolved 
out of an ancestral, more or less styliform, type of 
limb. 
There is another point to which it seems desirable 
to refer, namely, the use of group names based on 
our knowledge of existing animals in discussions on 
alezontology. The natural classification of animals 
is of course a concise method of summing up their 
