GENERATION AND INHERITANCE 289 



when I give a comprehensive sketch of the position and problems 

 of our present development in the realm of generation. 



The theme corresponds also to the general programme of the Board 

 of Managers of this Congress. It is their object to show, in the great 

 series of addresses which lie before us, a proof of the inseparable 

 connection of all branches of science. Our theme will show us, step 

 by step, how botanists and zoologists, students of the Protista, 

 anatomists and physiologists, work hand in hand when they inves- 

 tigate the general basic truths of their various sciences in the realm 

 of generation, as here, every step forward in one of these immediately 

 assists each of the others. The goal of truth, for which we seek from 

 various starting-points, is the great science of life, biology, to whose 

 investigation the separate ways lead. In another connection still, 

 we shall see how the development of biology is dependent, in more 

 than one connection, upon the development of other sciences, espe- 

 cially of physics and chemistry, and thus forms an integral limb in 

 the regular development of the great tree of knowledge. To give 

 a convincing example of this natural connection, the most important 

 discoveries which biology has made in the last hundred years were 

 made possible, in great part, by the development of physics. Con- 

 sider the advance in physical optics, and the technic connected there- 

 with, which through Abbe's labors gave us the compound microscope, 

 that wonderful instrument already brought to the highest perfection 

 and destined to overcome, in the rapid course of conquest, the new 

 world of the smaller micro-organisms. Embryological investigation, 

 especially, was seen to take a great spring forward the moment 

 physiologic knowledge showed that animals are built up of smaller 

 individuals, the cells, and thus are nothing more than communities 

 of innumerable, socially connected, elementary organisms. Embryo- 

 logy is indebted to the students of plant anatomy for the impulse 

 toward this new study which is built upon the knowledge of the 

 construction and origin of plants, based upon Schleiden's teaching. 

 For, standing upon Schleiden's shoulders, Schwann has shown the 

 dominion of the cell theory in the animal body. 



At this time the study of generation received its first scientific 

 basis. The beginning of individual life, the egg itself, is a cell, as 

 Schwann had already conjectured. The spermatozoa also, which in 

 the time of Johann Miiller were frequently looked upon as parasitic 

 organisms in the seminal fluid, comparable to infusoria, w r ere soon 

 explained by Kolliker as elementary parts of the animal, as they too 

 arise from cells. Thus the organism reproduces new individuals of 

 its own sort by loosing from their bonds single cells, as sexual pro- 

 ducts, which may begin an independent life in a new process of 

 development. While until now the progress came from the botanical 

 side, animal embryology, on the contrary, now began to have a fruit- 



