— ae: OY 
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TRANSACTIONS OF SECTION D. 843 
sequence of events is simpler or more straightforward. Its various organs and 
systems are formed in what is recognised as a primitive manner; and the develop- 
ment of each is a steady upward progress towards the adult condition. Food 
yolk, the great cause of distortion in development, is almost absent, and there is 
not the slightest indication of the former possession of a larger quantity. 
Concerning the later stages our knowledge is incomplete, but so much as has been 
ascertained gives no support to the suggestion of general degeneration. 
Our knowledge of the conditions leading to degeneration is undoubtedly 
incomplete, but it must be noticed that the conditions usually associated with 
degeneration do not occur. Amphioxus is not parasitic, is not attached when 
adult, and shows no evidence of having formerly possessed food yolk in quantity 
sufficient to have led to the-omission of important ancestral stages. Its small size 
as compared with other vertebrates is one of the very few points that can be 
referred to as possibly indicating degeneration, and will be considered more fully 
at a later point in my address. 
A consideration of much less importance, but deserving of mention, is that in 
its mode of life Amphioxus not merely differs as already noticed from those groups 
of animals which we know to be degenerate, but agrees with some, at any 
rate, of those which there is reason to regard as primitive or persistent types. 
Amphioxus, like Balanoglossus, Lingula, Dentalium, and Limulus, is marine, and 
occurs in shallow water, usually with a sandy bottom, and, like the three smaller 
of these genera, it lives habitually buried almost completely in the sand, into 
which it burrows with great rapidity. 
I do not wish to speak dogmatically. I merely wish to protest against a too 
ready assumption of degeneration; and to repeat that, so far as I can see, 
Amphioxus has not yet, either in its development, in its structure, or in its habits, 
been shown to present characters that suggest, still less that prove, the occurrence 
in it of general or extensive degeneration. 
In a sense, all the higher animals are degenerate ; that is, they can be shown 
to possess certain organs in a less highly developed condition than their ancestors, 
or even in a rudimentary state. 
Thus a crab as compared with a lobster is degenerate in the matter of its tail, 
a horse as compared with Hipparion in regard to its outer toes; but it is neither 
customary nor advisable to speak of a crab as a degenerate animal compared to a 
lobster ; to do so would be misleading. An animal should only be spoken of as 
degenerate when the retrograde development is well marked, and has affected not 
one or two organs only, but the totality of its organisation. 
It is impossible to draw a sharp line in such cases, and to limit precisely 
the use of the term degeneration. It must be borne in mind that no animal is at 
the top of the tree in all respects. Man himself is primitive as regards the 
number of his toes, and degenerate in respect to his ear muscles; and between 
two animals even of the same group it may be impossible to decide which of the 
two is to be called the higher and which the lower form. 
Thus, to compare an oyster with a mussel. The oyster is more primitive 
_ than the mussel as regards the position of the ventricle of the heart and its 
lett 
relations to the alimentary canal; but is more modified in having but a single 
adductor muscle ; and almost certainly degenerate in being devoid of a foot. 
Care must also be taken to avoid speaking of an animal as degenerate in 
regard to a particular organ merely because that organ is less fully developed 
than in allied animals. An organ is not degenerate unless its present possessor 
has it in a less perfect condition than its ancestors had. 
A man is not degenerate in the matter of the length of his neck as compared 
with a giraffe, nor as compared with an elephant in respect of the size of his front 
teeth, for neither elephant nor giraffe enters into the pedigree of man. A man is, 
_ however, degenerate, whoever his ancestors may have been, in regard to his ear 
muscles; for he possesses these in a rudimentary and functionless condition, 
which can only be explained by descent from some better equipped progenitor. 
_ Closely connected with the question of degeneration is that of the size of 
animals, and its bearing on their structure and development; a problem noticed 
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