MODERN BIOLOGY 533 



In a subsequent work on the course of development of an annelid he has 

 propounded a curious theory of its embryonic evolution in strong opposition 

 to Haeckel's gastrxa. theory and the coelom doctrine of the Hertwigs. He 

 starts with the sentence: " Es gibt kein tnittleres Keiinblatt," and adduces a 

 number of examples of how various organs that had been supposed to be 

 mesodermal, originate directly or indirectly from the ectoderm or entoderm. 

 At the same time he maintains that the form of one organ depends upon its 

 function and not upon its origin; "A comprehensive tissue-system is pos- 

 sible only on a physiological basis." These views were at the time at which 

 they were expressed (1886) so utterly opposed to those of his age that they 

 scarcely caused any sensation; their time came later, in connexion with the 

 altered view of evolution that has become prevalent in our day, which will 

 be described in a subsequent chapter. 



z. Cytology 



Development of microscopical cell-research 

 Microscopical cell-research is undoubtedly the branch of biology that re- 

 ceived the greatest stimulus during the last decade of the past century, and 

 that has seen the most important results and in many ways set its mark 

 upon the whole of biology in general. Its highly perfected methodics, with 

 its minute technical preparation of material for investigation, carefully 

 adapted to suit each particular case, and its careful microscopical study of 

 the smallest details, employing the highest possible magnifications, became 

 a characteristic feature of the research work of that period. The purely tech- 

 nical side of biology thereby received an entirely new character; whereas 

 formerly skill in dissection was the most essential qualification of the biolo- 

 gist, this ability now became to a certain extent superfluous, thanks to the 

 development of the technique of microtomy. On the other hand, the student 

 of cells, if he desires to create something new and to work independently, 

 must acquire a chemical knowledge of the means of fixing the tissues, as 

 well as a colour technique for the purpose of their further treatment. It was, 

 of course, possible for the whole of this method of research to degenerate 

 into a mere unintelligent dexterity, as biologists of the old school in par- 

 ticular called it, but it has also made possible more than any other method 

 the obtaining of results that have entirely transformed our conception of 

 the phenomena of life. 



We left cell research at the point to which Max Schultze had brought v 

 it — the knowledge of the cell as a limited quantity of protoplasm with 

 concomitant nucleus. Schultze is also remarkable inasmuch as in his cell 

 studies he was still working without a microtome; he brought cytology to 



