with food material as another, so that mobility is of no 

 advantage to it; but in order to assimilate this food it finds it 

 advantageous to assume an elongate or filiform shape in order 

 to expose as much of its protoplasm as possible both to nutrient 

 liquids and to light. 



Various parasitic protozoans, especially gregarines and fla- 

 gellates, living surrounded by nutrient material like a plant, 

 have secondarily assumed more or less the elongate plant-like 

 body form. 



In the Bryophyta and Pteridophyta an 8-celled embryo is 

 formed by the division of the original germ cell and its deriva- 

 tives in three planes each at right angles to the other two ; the 

 first cleavage plane divides this 8-celled embryo into two 

 4-celled halves each of which develops in a linear manner, one 

 half forming the roots and the other the stem and leaves. 



In the Phanerogamia a multicellular embryo is formed 

 with an outer (epidermal) layer and an inner mass of cells, this 

 embryo elongating and developing after the linear fashion of 

 the preceding. 



A flowering plant is composed of a large colony of indi- 

 viduals or phytons, each phyton being elongate and usually 

 also flattened, at least in part. In order to insure the maximum 

 efficiency for the individual phytons successive phytons are 

 developed radially so that one will not shade or otherwise 

 interfere with the functions of the others ; but the funda- 

 mentally radial arrangement of the phytons is modified, through 

 the fact that they are formed successively one after the other, 

 into a spiral, and a truly radial arrangement is only found 

 in the terminal groups of highly specialized phytons composing 

 the flowers. A true linear arrangement of the phytons never 

 occurs. 



In the animals the first step in advance over the protozoan 

 is through the formation of a globular morula or blastula, 

 this representing the first advance possible for organisms 

 with an inherent globular form and radial developmental 

 tendencies. In practically all animals part of the wall of the 

 blastula collapses forming a gastrula with an outer covering 

 and an inner lining of cells from one or both of which a few 

 or many cells, individually or as groups, become partially 

 or completely detached, each of the three categories of cells 



(400) 



