SYNOPSIS 481 



PAGE 



29. Diphyes. 



A free-swimming colony with polymorphic (nutritive, 

 reproductive, protective, and natatory) zooids 248 



30. Porpita. 



Extreme polymorphism of zooids giving the colony the 

 character of a single physiological individual 249 



V. SOLID AGGREGATES IN WHICH CELL-DIFFERENTIATION, AC- 

 COMPANIED BY CELL-FUSION, TAKES AN IMPORTANT PART iN 



PRODUCING GREAT COMPLEXITY IN THE ADULT ORGANISM. 



31. Polygordins. 



A triploblastic, ccelomate animal with metameric seg- 

 mentation : prostomium, peristomiuin, metameres, and 

 anal segment : besides ecto- and endoderm there is a 

 well developed mesoderm divided into somatic and 

 splanchnic layers separated by the ccelome : differenti- 

 ation of cells into fibres, &c. : muscle-plates formed as 

 cell-fusions : necessity for distributing system for supply 

 of food to parts of the body other than the enteric canal, 

 and for the removal of waste matters : circulatory, 

 respiratory, and excretory systems : high development of 

 nervous system brain and ventral cord, afferent and 

 efferent nerves : characteristic developmental stages 

 oosperm. polyplast, gastrula (diploblastic), trochosphere 

 (diploblastic with stomodeeum and protodseum), late 

 trochosphere (triploblastic but acoelomate) 268 



32. Mosses. 



Cell-differentiation very slight, but the type necessary to 

 lead up to ferns : sclerenchyma and axial bundle : dis- 

 tributing system rendered necessary by carbon dioxide 

 being taken in by the leaves, water and mineral salts bv 

 the rhizoids : alternation of generations the leafy plant 

 is the gamobium, the agamobium being represented by 

 the spore-producing sporogonium : developmental stages 

 oosperm and poiyplast, the latter becoming highly 

 differentiated to form the sporogonium 400 



33. Ferns. 



Extensive cell-differentiation : formation of fibres (elon- 

 gated cells) and vessels (cell-fusions) ; general differenti- 

 ation of tissues into epidermis, ground-parenchyma, and 

 vascular bundles : presence of true roots : the leafy plant 

 is the agamobium and produces spores from which the 

 gamobium, in the form of a small prothallus, arises : 

 developmental stages oosperm, polyplast, and phyllula 

 (leaf- and root-bearing stage) 4^1. 



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