YON BAER AND RISE OF EMBRYOLOGY. 123 



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 in- 

 terpretations, 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 embry- 

 ology 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 Whit- 

 man has been director since its foundation, in 1886, is to be men- 

 tioned 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 ernbry- 

 ological lines. 



Nearly all problems in anatomy and structural zoology are ap- 

 proached 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 con- 

 nection. 



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 re- 

 cent 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. 



