1893. BIQGLOGICAL THEQREIES. 199 
The statement that this stage in the development of a bird or a 
mammal is the modified remnant of the adu/t structure of the ancestor ; 
and that the ontogeny is even in part made up of a series of remnants of 
ancestral adult structures arranged in chronological order, is not only 
unjustified, but is demonstrably false. If any generalisation in the 
whole science of zoology is borne out by fact, it is the law of Von 
Baer with reference to animals living free only in later stages of 
development. That law claims a parallelism between the develop- 
ment of a fish and of a bird which is quite inconsistent with the re- 
capitulation theory, and completely consistent with the observed facts. 
The early stages of the fish embryo are very like those of the 
bird embryo. These two do correspond to each other. The state- 
ment that the embryonic structure of a bird follows a course 
which is, from beginning to end, roughly parallel with, but somewhat 
divergent from, the course followed by a fish, is borne out by the 
actual facts. A bird does not develop into a fish and then into a 
reptile and then into a bird. There is no fish stage, no reptile stage, 
in its ontogeny. The adult resembles an adult fish only very remotely, 
Every earlier stage resembles the corresponding earlier stage of the fish 
more closely. There is a parallelism between the two ontogenies. 
There is no parallelism between the ontogeny and the phylogeny of 
either a bird or any other animal whatever. A seeming parallelism 
will fall through when closely examined. 
Each transient stage in the development of any individual is a 
modification of the corresponding stage of development of its ancestors. 
It is in no case a modification of the adult stage of the ancestor. The 
adult stage of a bird, and no other, corresponds to the adult stage of 
the fish-like ancestors (if it ever had such ancestors). 
The stalked “pentacrinoid” larva of Antedon (=Comatula) is 
a modified equivalent of the stalked larva of the ‘“ pentacrinoid ” 
ancestor (if ever there was such an ancestor), and not the modified 
equivalent of the adult ancestor. The possession of a stalk in early 
stages of development appears to be an advantage, and hence the 
specific constitution which determines the development through a 
stalked stage has been preserved by Natural Selection. There is no 
evidence whatever to justify such mystical conceptions as those 
involved in even the most reasonable forms in which the recapitulation 
theory has been applied to this case. 
The promise which the theory gave of serving as the guide to 
knowledge of past history, without the labour involved in paleon- 
tological research, was, indeed, tempting : and when the “royal road 
to learning’? had been shown by it, it is not surprising that some 
zoologists should have entered for the race along this road. To what 
goal that road has led may be learned by a comparison of the 
numerous theories as to the ancestry of ‘‘ chordata”’ which have been 
put forward by those who adopted the theory without enquiring as to 
its validity. 
