2 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



the seventeenth and eighteenth centuries that Spallanzani, Redi, Swam- 

 merdam, and Rosel von Rosenhof, attempted to demonstrate by experi- 

 ment the error of the theory of spontaneous generation. With the 

 pubHcation of the work of Von Baer the modern phase of embryology 

 begins. It was Von Baer who elaborated Pander's idea of the three germ 

 layers in the early embryo from which the later organs are developed. 

 He also called attention to the greater similarity that exists between 

 embryos of related groups than between adults and thus suggested what 

 later became known as the "recapitulation theory," or "the biogenetic 

 law/' which is attributed to F. Miiller and E. Haeckel. 



Among the earlier works dealing with the embryology of insects may 

 be mentioned that of Herold (1815) on the Lepidoptera, of Hummel (1835) 

 on the roach, and of Kolliker (1843) on a comparative study of the 

 development of insects and vertebrates. These researches were followed 

 by Weismann's (1863) work on the Diptera which represents for its time 

 an outstanding contribution to our knowledge of the embryology of this 

 group of insects. The work of Mecznikow and Biitschli on the honeybee 

 belongs to this period. In the year 1871 a paper on the embryology of 

 worms and arthropods by Kowalewsky appeared, a work of great merit, 

 in which the method of cutting sections of tissues, previously fixed and 

 embedded in paraffin, was used. During the thirty years that followed, 

 numerous and important contributions to the subject of arthropod 

 embryology were made by both European and American investigators. 

 Among prolific European writers of this period may be mentioned 

 Carriere, Cholodkowsky, Graber, Heider, Heymons, Korschelt, and 

 Nusbaum. For the same period the works of the American zoologists 

 Ayers, Claypole, Knower, Packard, Patten, Ryder, Wheeler, and Wood- 

 worth are noteworthy. Wheeler's papers on the development of the 

 Orthoptera are especially outstanding. 



The strong interest that has been aroused in vertebrate embryology 

 by the recent experimental work on the amphibians by Spemann and his 

 associates is reflected in a greatly increased activity in the study of the 

 normal embryonic development of insects, which is a prerequisite to 

 experimental work. The pioneer experimental studies of Wheeler, 

 Megusar, and Hegner have been followed up by those of Reith, Seidel, 

 Pauli, and others in Europe and by those of Brauer, Child, How- 

 land, King, Shull, Slifer, Weiss, and others in the United States. 



All these investigations cannot fail to impress one with the necessity 

 for a study of the developmental processes from the standpoint of genetics, 

 physiology, and cytology in order to obtain an adequate conception of 

 what is involved. A consideration of the first and second of these exten- 

 sive topics lies outside the scope of this text. As for the third, only so 

 much of it will be included here as may be required for an understanding 



