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CHAPTER IX. 



PROTECTING AND SUPPORTING STRUCTURES. 



WITH the exception of such simple forms as Prot- 

 amceba, even the lowest Protozoa exhibit some kind 

 of difference between the outer parts of the cell that 

 have to bear with the jars and dangers of external 

 agencies, and the inner parts that are protected from 

 them. In Amoeba itself we can recognise (Fig. 1) 

 a difference between the outer ectosarc and inner en- 

 dosarc. The former, from our present point of 

 view, may be merely said to be firmer ; but we have 

 to note that the ectosarc of such Amoebae as live in 

 moist earth is much firmer than in those which live in 

 water. But the group of which the Amo3ba is the 

 simplest representative is not without parts which 

 clearly form supports for the protoplasm of the cell : 

 these are firmer structures, which may be called 

 skeletons. 



In the present chapter, then, we shall chiefly denl 

 with skeletal structures, whether internal or external, 

 but we shall have also to speak of other offensive 

 and defensive organs. 



The ectosarc of the Amoeba leads to the definite 

 cuticle of the Infusorian; but the Sarcodina are nob 

 without external defensive structures. The simplest 

 condition may be found in such a form as Gromia 

 (Fig. Ill), where the ectosarc forms an organic layer of 

 a substance like chitin, which, while it envelops the 

 general body mass, may be itself flowed over by the 

 contained protoplasm. In such a test as this there is 

 a single large orifice at one end. This chitinous test 

 varies considerably in thickness and consistency in 



