It is not so generally known that he was also a great investigator, producing a large amount of purely technical researches. After his death a memorial edition of his scientific memoirs was published in four large quarto volumes. The extent of his scientific output when thus assembled was a surprise to many of his co-workers in the field of science. His other writings of a more general character have been collected in fourteen quarto volumes. Some of the essays in this collection are models of clear and vigorous English style. Mr. Huxley did an astonishing amount of scientific work, especially in morphology and palæontology. Those who have been privileged to look over his manuscripts and unpublished drawings in his old room at South Kensington could not fail to have been impressed, not only with the extent, but also with the accuracy of his work. Taking Johannes Müller as his exemplar, he investigated animal organisms with a completeness and an exactness that have rarely been equaled.
An intimate account of his life will be found in The Life and Letters of Thomas Henry Huxley, by his son.
Haeckel.—Ernst Haeckel, of Jena, born in 1834 (Fig. 122), was one of the earliest in Germany to take up the defense of Darwin's hypothesis. As early as 1866 he applied the doctrine of evolution to all organisms in his Generelle Morphologie. This work, which has been long out of print, represents his best contribution to evolutionary thought. He has written widely for general readers, and although his writings are popularly believed to represent the best scientific thought on the matter, those written for the general public are not regarded by most biologists as strictly representative. As a thinker he is more careless than Huxley, and as a result less critical and exact as a writer.
Fig. 122.—Ernst Haeckel, Born 1834.
There can be no doubt that the germs of evolutionary thought existed in Greek philosophy, and that they were retained in a state of low vitality among the mediæval thinkers who reflected upon the problem of creation. It was not, however, until the beginning of the nineteenth century that, under the nurture of Lamarck, they grew into what we may speak of as the modern theory of evolution. After various vicissitudes this doctrine was made fertile by Darwin, who supplied it with a new principle, that of natural selection.
The fruits of this long growth are now being gathered. After Darwin the problem of biology became not merely to describe phenomena, but to explain them. This is the outcome of the rise and progress of biology: first, crude and uncritical observations of the forms of animated nature; then descriptive analysis of their structure and development; and, finally, experimental studies, the effort to explain vital phenomena, an effort in which biologists are at present engaged.