No. 381.] A HALF-CENTURY OF EVOLUTION. 625 
epigenetic view is largely due to exact investigation and 
modern methods of research, but more especially to the results 
of modern embryology and to the fairly well digested facts we 
now have relating to the development of one or more types of 
each class of the animal kingdom. 
To use a current phrase, the evolution theory as now held 
has come to stay. It is the one indispensable instrument on 
which the biologist must rely in doing his work. It is now 
almost an axiomatic truth that evolution is the leaven which 
has leavened the whole lump of human intellectual activity. It 
is not too much to claim that evolutionary views, the study of 
. origins, of the beginning of organic life, the genesis of mental 
phenomena, of social institutions, of the cultural stages of dif- 
ferent peoples and of their art, philosophy, and religion, — that 
this method of natural science has transformed and illuminated 
the philosophy of the present half-century. 
“a caterpillar at first scarcely as large as a bit of thread, contains its own tegu- 
ments threefold and even eightfold in number, besides the case of a chrysalis, and 
a complete butterfly, all lying one inside the other.” This view, however, we find 
is not original with Lacordaire, but was borrowed from Kirby and Spence without 
acknowledgment. These authors, in their /xtroduction to Entomology (1828), 
combated Herold’s views and stoutly maintained the old sired z Swammer- 
dam. They based their opinions on the fact, then known, that ain parts of 
the imago occur in the caterpillar. On the other hand, Herold pare Ate the 
Successive skins of the pupa and imago existed as germs, holding that they are 
formed successively from the rete meer which we sup t the 
hypodermis of later authors. In a slight degree the Swammerdam-Kirby and 
Spence doctrine was correct, as the imago does arise from germs, ż.e., the imaginal 
discs of Weismann, while this was not discovered by Herold, though they do at 
the outset arise from the hypodermis; his rete mucosum. Thus there was a grain 
of truth in the Swammerdam-Kirby Ee Spence doctrine, and also a mixture of 
truth and error in the opinions of Hero 
The discovery by Weismann of the oe discs or buds of the imago in the 
Maggot of the fly, and his theory of histolysis, or of the more or less opta 
destruction of the larval organs by a gradual process, and his observation of t 
process of building up of the body of the imago from the previously latent aiii 
uds, was one of the triumphs of modern biology. It is therefore not a little 
Strange to see him at the present day advocating a return to the preformation 
views of the last century in the matter of heredity. Of course it goes without 
saying, as has always been recognized, that there is something in the constitution 
of one egg which seein its becoming an insect, and in that of another which 
PEPI it to produce a chick. 
1 It is worthy to mention that just fifty years ago, in his Future of Science, 
written in 1848, at the age of 25, Renan, who first among philosophers and stu- 
