34 ESSENTIALS OF BIOLOGY 



We now form the conceptions of Orders of Individuality and 

 successive integrations. 



(a) Individuals of the First Order. The Protists (cells), unicellu- 

 lar organisms, 

 (z) The First Integration. Protists (cells) coalesce to form 

 the simple, unisegmental body — such as that of a 

 Hydra, giving — 

 {b) Individuals of the Second Order such as the Hydra, or 

 sea-anemone. Multicellular and plurisegmental. 

 {ii) The Second Integration. Segments coalesce to form 

 the pluri-segmental body — such as the siphono- 

 phone, vertebrate, etc., giving 

 {c) Individuals of the Third Order. All the higher animals. 



Multicellular and plurisegmental. 

 It is not altogether fanciful to see in the animal communities 

 (the gregarious herd, the insect hive, the human society) a fourth 

 order of individuality. A third integration has been effected 

 by instinctive and intelligent activities, while in the human society 

 the individuals integrate by traditions, laws, inhibitions, taboos, 

 etc. In the insect communities there are structurally differ- 

 entiated castles. In human societies castes have a basis in tradi- 

 tion. In these higher integrations behaviour is the main factor. 



11. ON TYPES OF ANIMAL STRUCTURE 

 We attempt here to reduce the diversity of animal forms to a 

 few general types. Detail is neglected and the morphology is 

 idealized — to some extent. 



iia. The Unicellular Type. The animal is either (and 

 typically) a single organic cell, or a loosely compacted colony of 

 cells that are alike in most respects (see Fig. i). 



lib. The Sponge Type. The sponge body may not have 

 any essential and definite shape. It has rough upper and lower 

 symmetry in that it is fixed to some support, such as a stone on 

 the sea bottom. In its most simple form it is a sac. At the 

 upper part of the sac there is, typically, a large opening, or 

 osculum. Everywhere else there are pores in the wall of the sac. 

 The pores lead into canal-systems and water, entering the latter 

 by the pores, leaves the sponge body by the osculum, or oscula. 

 The canals are mostly lined by a layer of '* collar-cells " and the 



