392 Coe — A Century of Zoology in America. 



corresponding with the four pairs of chromosomes which 

 the cells of this fly possess. 



Comparative Physiology. 



None of the experimental fields has been of greater 

 importance in zoological progress than that which con- 

 cerns the functions of the various organs. Without this 

 companion science morphology and comparative anatomy 

 would have become unintelligible. American investiga- 

 tors, among whom Gr. H. Parker stands prominent, have 

 taken a leading part in this field also. 



Neurology. — The physiological analysis of the com- 

 ponents of the nervous system, both in vertebrates and 

 invertebrates, is another important branch of experimen- 

 tal biology. The 28 volumes of the Journal of Compara- 

 tive Neurology attest the large influence that American 

 investigators have had in the development of this science. 



Regeneration. — Experimental studies on the powers 

 of regeneration in plants and animals have been made 

 from the earliest times. During the past few years, how- 

 ever, there has been made a concerted attempt to analyze 

 the factors which determine the amount and rate of 

 regeneration. Much progress has been made toward the 

 postulation of definite laws applicable to the regenerative 

 processes of the parts of each organism. The critical 

 analyses of Child have been particularly stimulating. 



Tissue Culture. — Another line of experimental work 

 which has been developed within the past few years by 

 Harrison, Carrell, and others is the culture of body 

 tissues in artificial media. These experiments have 

 included the cultivation in tubes or on glass slides of the 

 various tissues of numerous species of animals. They 

 have yielded much information regarding the structure, 

 growth and multiplication of cells, the formation of tis- 

 sues, and the healing of wounds. 



Transplantation and Grafting. — Closely associated 

 experiments consist in the transplantation of organs or 

 other portions of the body to abnormal positions, to the 

 bodies of other animals of the same species or of other 

 species. In this way much has been learned about the 

 potentiality of organs for self-differentiation, for regula- 

 tion, for regeneration and for compensatory adaptations. 

 The experiments have shown, further, the independence 

 of soma and germplasm and have revealed the nature of 

 certain organs whose functions were previously obscure. 



