74 



GBNEKAL PHYSIOLOGY 



cells. But the origin of the Myxomycete plasmodia renders such 

 a view uncertain. Myxomycetes reproduces by spores, i.e., by small 

 microscopic capsules, the shells of which burst and give exit m 

 each case to a small naked cell, which is capable of changing its 

 shape and is provided with one nucleus (Fig. 15, a, h, c). A very 

 large number of the spores always coexist and many separate cells 

 creep out at the same time. These cells soon creep together, 

 coalesce, and thus form a larger, unitary, protoplasmic mass, which 

 contains a number of nuclei (Fig. 15 e,f). The mass grows by its 

 own nutritive efforts, the nuclei multiply by division, and thus 



Fig. 15. — /, Aethaliutn septicuni ; a piece of a reticulate Myxomycete plasraodium, natural size. 

 II, Chondrioderma dijforme ; /, piece of a Plasmodium ; a, a spore, b, the same, swelling, c, the 

 contents of the spore is creeping out ; d, tlie spore has changed into a flagellated cell ; e, the 

 flagellated cells have transformed themselves into anxoebse, which are creeping together again 

 to form a Plasmodium. (// After Strasburger.) 



arises finally the large, reticulate ^alasmodium. This plasmodium, 

 therefore, although representing a unitary protoplasmic mass con- 

 taining many nuclei and without cell-boundaries, has arisen from 

 many single cells. Hence, strictly, it is not proper to consider the 

 Plasmodium of Myxomycetes as a multinucleate cell ; at the same 

 time it is not justifiable to speak of it as a genuine tissue, for 

 no cell-boundaries are marked out for the single nuclei. A special 

 name, therefore, has been created for these intermediate stages 

 between the single cell and the tissue, and they have been called 

 syncytia. 



B. THE MORPHOLOGICAL NATURE OF LIVING SUBSTANCE 



1. The Form and Size of the Cell 



The chief fact that has stood in the way of a consistent ex- 

 tension of the cell-theory and one that still presents at first the 

 greatest difficulties to all who study the finer structure of organ- 

 isms, is the astonishing variety of forms in which the elementary 

 constituent of organisms appears. The forms of the different 



