172 
ANIMAL PEDIGREES. 
Aug., 1891. 
means of escape from difficulties arising through theoretical 
views concerning the relation between vertebrates and 
invertebrates. 
Amphioxus itself, so far as I can see, shows in its 
development no sign of degeneration, except possibly with 
regard to the anterior gut diverticula, whose ultimate fate is 
not altogether clear. With regard to the earlier stages of 
development, concerning which, thanks to the patient investi¬ 
gations of Kowalevsky and Hatschek, our knowledge is precise, 
there is no animal known to us in which the 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 development 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 posses¬ 
sion 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 ver¬ 
tebrates, is one of the very few points that can be referred to 
as possibly indicating degeneration, but by no means proving 
its occurrence. 
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 per¬ 
sistent 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 com¬ 
pletely 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 degenera¬ 
tion. 
