Aug., 1891. 
ANIMAL PEDIGREES. 
171 
About such cases there is no doubt; but we are asked to 
extend the idea of degeneration much more widely. It is 
urged that we ought not to demand direct embryological 
evidence before accepting a group as degenerate. We are 
reminded of the tendency to abbreviation or to complete 
omission of ancestral stages of which we have quoted examples 
above ; and it is suggested that if such larval stages were 
omitted in all the members of a group we should have no 
direct evidence of degeneration in a group that might really 
be in an extremely degenerate condition. 
Supposing, for instance, the free larval stages of the 
solitary Ascidians were suppressed, say through the acquisition 
of food yolk, then it is urged that the degenerate condition of 
the group might easily escape detection. The supposition is 
by no means extravagant ; food yolk varies greatly in amount 
in allied animals, and cases like Hylodes. or. amongst Ascidians, 
Pyrosoma, show how readily a mere increase in the amount of 
food yolk in the egg may lead to the omission of important 
ancestral stages. 
The question then arises whether it is not possible, or even 
probable, that animals which now show no indication of 
degeneration in their development are in reality highly degen¬ 
erate, and whether it is not legitimate to suppose such 
degeneration to have occurred in the case of animals whose 
affinities are obscure or difficult to determine. 
It is more especially with regard to the lower vertebrates 
that this argument has been employed; and at the present 
day zoologists of authority, relying on it, do not hesitate to 
speak of such forms as Amphioxus and the Cyclostomes as 
degenerate animals, as wolves in sheep’s clothing, animals 
whose simplicity is acquired and deceptive rather than real 
and ancestral. 
I cannot but think that cases such as these should be 
regarded with some jealousy ; there is at present a tendency 
to invoke degeneration rather freely as a talisman to extricate 
us from morphological difficulties ; and an inclination to accept 
such suggestions, at any rate provisionally, without requiring 
satisfactory evidence in their support. 
Degeneration of which there is direct embryological 
evidence stands on a very different footing from suspected 
degeneration, for which no direct evidence is forthcoming; 
and in the latter case the burden of proof undoubtedly rests 
with those who assume its existence. 
The alleged instances among the lower vertebrates must 
be regarded particularly closely, because in their case the 
suggestion of degeneration is admittedly put forward as a 
