CHAPTER VII 

 THE MULTICELLULAR ORGANISM 



The student of Nature wonders the more and is astonished 

 the less, the more conversant he becomes with her operations; 

 but of all the perennial miracles she offers to his inspection, 

 perhaps the most worthy of admiration is the development of 

 a plant or animal from its embryo. Huxley. 



IT has been pointed out that all organisms consist of one 

 free living cell or of many cells, and some idea has been 

 gained of unicellular forms from Sphaerella, Paramecium, and 

 the Bacteria which were selected to illustrate various types 

 of nutrition. We are now in a position to consider the origin 

 and organization of the individual in the METAZOA and 

 METAPHYTA, as the multicellular animals and plants are 

 sometimes called. 



Every individual, with exceptions to be noted later, begins 

 its existence as a single cell which has been set free as such 

 from the parent; or which has been formed at fertilization 

 by the fusion of two cells, or GAMETES, each typically de- 

 rived from a separate parent individual. The former is 

 known as UNIPARENTAL, or ASEXUAL, reproduction and the 

 latter as BIPARENTAL, or SEXUAL, reproduction. Both 

 asexual and sexual methods are widespread among plants and 

 animals, frequently alternating in regular sequence in the 

 same species to give what is termed an ALTERNATION OF 



GENERATIONS. 



The most remarkable fact about the reproductive cells is the 

 inherent power of each to develop into a replica of the parent 



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