CONTINUITY OF LIFE 



67 



case of Volvox ; another is shown in Fig. 28, B, which represents 

 a syncytial epithelium. 



On the other hand, in some of the lower organisms the 

 Myxomycetes, slime-fungi or Mycetozoa, as they are variously 

 called numerous originally separate Amoeba-like individuals 

 may fuse together to form plasmodia, which may continue to 

 feed and grow and undergo nuclear division until they form great 

 sheets of living protoplasm containing perhaps hundreds or 

 thousands of nuclei (Fig. 29). These and similar facts, how- 

 ever, interesting and 

 instructive as they un- 

 doubtedly are, cannot 

 be regarded as con- 

 stituting a serious 

 invalidation of the cell 

 theory. 



There is no more 

 fundamental or more 

 stimulating conception 

 in the domain of bio- 

 logical science than 

 that of the continuity 

 of life as formulated by 

 this theory. We have 

 to imagine the whole 



Organic WOrld as C011- 

 . . 



sisting of a continuous 



cfroarn nf liin'no- rivr. 

 living pl( 



toplasm, which com- 



, . n 



menced to now many 

 millions of years ago and has continued without interruption 

 ever since. At every cell-division the stream branches and 

 physical continuity is more or less completely interrupted, but 

 this in no way invalidates the conclusion that if all living things 

 did not actually have a common origin in a single primordial 

 protoplasmic unit, they probably at least originated from several 

 such units which themselves arose under unknown conditions 

 from inorganic matter. 



The modern science of cytology, which is contrasted with 

 histology as the study of individual cells rather than that of 

 tissues or cell combinations, and which is yielding such important 



F 2 



FIG. 28. 



A single-layered epithelium with very distinct cell- 

 outlines, from the brain of a reptile (Sphenodon 



punctatus), x 750. 



A syncytial epithelium, without cell-outlines, from 

 another part of the brain of the same animal 



x 750. 



nu. nuclei. 



