82 BIOLOGICAL LECTURES. 



drawn into the center of the animal and imbedded in the 

 cytoplasm. 



In the same way the excretophores get loaded with excretory 

 granules, and these are further disposed of in the following 

 ways : 



The intracoelomic excretophores arrive, after they are well 

 loaded with excretory material, in the neighborhood of the 

 nephrostomes and disintegrate there. Their contents, liquefied 

 plasma, nuclei, and excretory granules, are drawn into the fun- 

 nel by a ciliary current. From the inner cavity of the funnels 

 the waste products are brought into the adjoining nephridial 

 cells, and being conveyed through the entire length of the 

 nephridium, they finally get to the exterior. 



The extracoelomic excretophores wander about between the 

 tissues and pick up the waste products which are discharged 

 from the different elements. A great quantity of waste prod- 

 ucts is produced by the contents of the small blood-vessels and 

 the capillaries, and we may observe the excretophores gather 

 around these organs and pick up small granules which lie on 

 the surface of the walls of the capillaries. After they are 

 loaded with waste products they begin to wander toward the 

 dorsal surface of the animal, which wandering is due to a posi- 

 tive chemotropism towards oxygen. The dorsal layers of the 

 skin are the seat of capillary respiration, and are therefore to 

 be regarded as a hearth of free oxygen, towards which the 

 excretophores wander. 



As soon as these cells arrive below the epidermis, they dis- 

 integrate, and their remains constitute the pigment. Our main 

 task is to explain these phenomena, to study the minute 

 mechanism and chemism of excretion. 



The first question which we have to answer is: What changes 

 take place in the excretophores when they pick up excretory 

 granules ? 



Before I can answer this question I have to speak of one 

 property of protoplasm which to my knowledge has never been 

 emphasized, and by the conception of which we may treat a 

 series of seemingly widely different phenomena of cellular life 

 under one common heading. This property I call, in the 



