feature of technique, and the success of an investigation may depend, very largely, on the care exercised in the use of reagents and dyes, and the mechanical part of getting sections in shape for observation. Investigations of an earlier period were now repeated with greater refinement of technique, and the result was, a change not only in interpretations, but often in the points of observation.
Establishment of Marine Biological Laboratories.—Among other influences which have contributed to the advancement of embryology—as well as to all biology—has been the establishment of fully equipped sea-side laboratories. These have supplied facilities for working where developing forms are most abundant and most diversified. Also, as distributors of prepared material, they have made a wide range of forms available to investigators. The famous 'Stazione Zoologica' founded by Dohrn in 1872, and still under his direction, has exercised a powerful influence. Not only have numerous researches in embryology been carried on there, but, also, prepared material has been shipped to investigators in all parts of the world. Balfour was one of the earliest to avail himself of the opportunities at the Naples Station. The Marine Biological Station at Wood's Hole, Mass., of which Whitman has been director since its foundation, in 1886, is to be mentioned as second only to that of Naples for the extent of its influence and quality of its work. The many other similar laboratories in this country and abroad have aided in the great advance along embryological lines.
Nearly all problems in anatomy and structural zoology are approached from the embryological side, and, as a consequence, the work of the great army of anatomists and zoologists has been in a measure embryological. Many of them have produced beautiful and important work, but the work is too extended to admit of review in this connection.
Oscar Hertwig, of Berlin, whose portrait is shown in Fig. 12, is one of the representative embryologists of Europe, and lights of the first magnitude in this country are Brooks, Minot, Whitman and E. B. Wilson.
Although no attempt is made to review the researches of the recent period, we can not pass entirely without mention the discovery of chromosomes and of their reduction in the ripening of the egg and in the formation of sperms. This has thrown a flood of light on the phenomena of fertilization, and has led to the recognition of these bodies as, probably, the bearers of heredity.
The work of the late Wilhelm His, whose portrait is shown in Fig. 13, is 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.
