102 BIOLOGY AND ITS MAKERS 



Von Baer had founded embryology by his great work on the 

 development of animals in 1828, before the investigations of 

 Dufour, but it was reserved for Newport to recognize its 

 great importance and to apply it to insect anatomy. He saw 

 clearly that, in order to comprehend his problems, the anat- 

 omist must take into account the process of building the body, 

 as well as the completed architecture of the adult. The in- 

 troduction of this important idea made his achievement a 

 distinct advance beyond that of his predecessors. 



Leydig. — Just as Newport was publishing his conclusions 

 the cell-theory was established (in 1838-39); and this was 

 destined to furnish the basis for a new advance. The in- 

 fluence of the doctrine that all tissues are composed of similar 

 vital units, called cells, was far-reaching. Investigators began 

 to apply the idea in all directions, and there resulted a new 

 department of anatomy, called histology. The subject of 

 insect histology was an unworked field, but manifestly one 

 of importance. Franz J.eydig (for portrait see p. 175) 

 entered the new territory with enthusiasm, and through his 

 extensive investigations all structural studies upon insects 

 assumed a new aspect. In 1864 appeared his Vom Bait des 

 Thierchen Korpers, which, together with his special articles, 

 created a new kind of insect anatomy based upon the micro- 

 scopic study of tissues. The application of this method of 

 investigation is easy to see; just as it is impossible to under- 

 stand the working of a machine without a knowledge of its 

 construction, so a knowledge of the working units of an organ 

 is necessary to comprehend its action. For illustration, it is 

 perfectly evident that we can not understand what is taking 

 place in an organ for receiving sensory impressions without, 

 first understanding its mechanism and the nature of the 

 connections between it and the central part of the nervous 

 system. The sensory organ is on the surface in order more 

 readily to receive impressions from the outside world. The 



