232 BIOLOGY AND ITS MAKERS 
zoodlogists has been in a measure embryological. Many of 
them have produced beautiful and important researches, but 
thework is too extended to admit of review in this connection. 
Oskar Hertwig, of Berlin (Fig. 70), is one of the repre- 
sentative embryologists of Europe, while, im this country, 
lights of the first magnitude are Brooks, Minot, Whitman, 
E. B. Wilson, and others. 
Although no attempt is made to review the researches of 
the vecent period, we cannot pass entirely without mention 
the discovery of chromosomes, and of their reduction in the 
ripening of the egg and in the formation of sperm. This has 
thrown a flood of light on the phenomena of fertilization, and 
has led to the recognition of chromosomes as probably the 
bearers of heredity. The nature of fertilization, investigated 
by Fol, O. Hertwig, and others, formed the starting-point for 
a series of brilliant discoveries. 
The embryological investigations of the late Wilhelm His 
(Fig. 71) are also deserving of especial notice. His luminous 
researches on the development of the nervous system, the 
origin of nerve fibers, and his analysis of the development of 
the human embryo are all very important. 
Recent Tendencies. Experimental Embryology.—Soon 
after the publication of Balfour’s great work on “‘ Comparative 
Embryology,” a new tendency in research began to appear 
which led onward to the establishment of experimental em- 
bryology. All previous work in this field had been concerned 
with the structure, or architecture, of organisms, but now the 
physiological side began to receive attention. Whitman has 
stated with great aptness the interdependence of these two 
lines of work, as follows: “‘ Morphology raises the question, 
How came the organic mechanism into existence? Has it 
had a history, reaching its present stage of perfection through 
a long series of gradations, the first term of which was a 
relatively simple stage? The embryological history is traced 
