316 ORGANIC GROWTH sec. 



without organs were yet unknown ; tliey were first discovered 

 by the aid of the microscope. They are represented by the 

 simple minute morsels of protoplasm to which Haeckel has 

 given the name of Monera {ijiovqpr)^ simple). These are cells 

 possessing neither nucleus nor investing membrane, which 

 nevertheless lead an independent existence, and of some of 

 which the whole life cycle is known. In these beings organs 

 only appear at the moment they are needed, and at any part 

 of the body, they are not developed beforehand, and have no 

 definite shape. These organs are processes of the protoplasm 

 of variable form, "false feet," or pseudopodia, by means of 

 which the body crawls about or takes in food. When the 

 cell returns to a condition of rest the pseudopodia flow back 

 again, are withdrawn and disappear, while the body assumes 

 a spherical shape. The conception of an organ as a part of 

 the body constructed for a definite function is therefore not 

 applicable to these pseudopodia, it applies only to the per- 

 manent instruments of the more complex beings which alone 

 are in the full sense of the word organisms. 



In the creatures next above these in the animal scale, in 

 the Amoebse, a permanent organ first appears, namely, the 

 cell-nucleus. Besides this there are also present the so-called 

 contractile vacuoles, which, however, in some cases appear 

 now in one place, now in another, and then again disappear, 

 and whose claim to be considered permanent organs is there- 

 fore doubtful. Locomotion and the inception of food are 

 still effected by pseudopodia. In the next stage in the series 

 of unicellular animals a membrane appears as a permanent 

 organ, while cilia take the place of the pseudopodia, to which 

 are necessarily added a mouth for taking in food, and in 

 many cases an anus. The body is still in most cases capable 

 of changing its form, and owes this power sometimes to the 

 differentiation and modification of the outermost layer of 

 protoplasm lying immediately beneath the membrane, this 



