Eyes of Molluscs and Arthropods. 705 



Chapter TI '. Theoretical Bemarks Concerning the Origiu and 

 Function of Sense Organs and of Animai Pigment. 



Living- bodies are distiiiguished by their power to absorb matter 

 and euergy, and from them produce high Compounds, by whose disin- 

 tegratiou force is liberated as motion. This sequence of events is 

 vitality. It consists of four processes: (1) absorption of matter; (2) 

 absorption of energy ; (3) production of high Compounds ; (4) the fall of 

 these Compounds, producing motion. An inseparable result of vitality, 

 but not a vital process, is excretion, or the discharge of disenergized 

 matter. We have only to deal with the second of these processes, the 

 absorption of energy, or dynamophagy, and more especially with 

 the absorption of solar energy, orheliophagy. 



The most primitive and universal method of dynamophagy is 

 the absorption of solar energy by Chlorophyll; but in animals we have 

 good reason to believe that various forms of energy are absorbed in 

 several ways : (1 ) solar energy, by means of pigment or by nerve fibres; 

 (2) energy of sound vibrations, by auditory hairs ; (3) energy of coarser 

 vibrations, of pressure, contact, or movement, by tactile hairs; and (4) 

 that of gases, Solutions, or chemical Compounds, by means of so-called 

 taste cells. All these processes in their higher stages suppose the pre- 

 sence of a nervous system, and, since the development of nerves and 

 sense organs go band in band , we must have some idea of how a 

 nervous system could have originated, if we would foUow the develop- 

 ment of sense organs. 



Let US suppose that we have before us the simplest form of a multi- 

 cellular animai, then all the cells will be alike, eachperforming for itself 

 all the functions necessary for its existence ; each cell would absorb its 

 own matter and the energy, or Stimuli, necessary for its conversion into 

 living Compounds. The relation between the matter and energy ab- 

 sorbed is a Constant one. The cells would tend to vary in two direc- 

 tions : (1) towards the absorption of more energy, or (2) of more matter. 



1 The following chapter is not so much an attempt to discuss the evidence for, 

 er against any conclusion, as to make clear my own opinion upon the subject. With 

 this object in view, I have omitted the discussion of several doubtful questions, 

 and I have also made preparatory suppositions, which it is neither the place nor 

 my Intention to discuss here. My Statements have been made positive for the sake 

 of brevity and clearness, but they must be regarded as suggestions, for which I 

 can, as yet, bring no proof, rather than as positive assertions. 



Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. VI. 47 



