MORPHOLOGY OF ANIMALS 



However, there may be exceptions to each of these criteria 

 and then the decision as to whether the organism is a plant or 

 animal may be difficult if not impossible to make. 



II. SUBDIVISIONS OF ANIMALS AND PLANTS 



Both animals and plants are subdivided into one-celled 

 and many-celled forms and each of these is further subdi- 

 vided as is shown in the tables, pages 1 1, 12, 13 of the Labo- 

 ratory Directions, and at the end of this Synopsis. 



1. Protophyta are one-celled plants, and Protozoa are one- 

 celled animals in which the entire body consists of a single 

 cell, which may be independent, or may be joined with 

 others like itself to form a colony of similar cells. 



2. Metaphyta are many-celled plants and Metazoa are 

 many-celled animals in which the body consists of many 

 cells which differ more or less from one another. 



3. Transitions from Unicellular to Multicellular forms. In 

 plants there is a complete series 'of intermediate forms 

 from the single cell to the solid aggregate of cells as fol- 

 lows: 



(^) Single cell (e.g. Spherella), 



(^) Linear aggregate of cells (e.g. Spirogyra), 



(r) Superficial aggregate of cells (e.g. Ulva), 



(<i) Solid aggregate of cells (e.g. mushrooms and all 



higher plants). 



Among animals a great gap exists between Protozoa 

 and Metazoa, there being no animals living today that are 

 intermediate between the two. However, all Metazoa, in 

 their development from the egg, pass from a unicellular to 

 a multicellular condition through the cleavage stages^ the 

 bias tula and tht gas trul a (Fig. 1). 



: 2 : 



