122 RAMBLES AND REVERIES. 



or put it into a flinty skeleton, and it becomes a 

 polycystin ; or range a mass of them together, and 

 build around them walls and girders of flint, and a 

 sponge is the result. The jelly animal is the same 

 in every case, and all these agree in having no special 

 limbs, any portion of the body fulfilling, in turn, 

 the functions of arms, legs, mouth, or stomach. It 

 is clear then that we are dealing with the lowest 

 forms of animal life, and all the creatures just enu- 

 merated amoeba, foraminifera, polycystins, sponge 

 are grouped together in one large sub-kingdom, 

 called Protozoa, which, as the name imports, stands 

 on the lowest rung of the zoological ladder. 



For more precise details respecting the structure 

 of amoeba we had better look at Nicholson's 

 Zoology. We learn there that the body of this 

 animal is composed of gelatinous sarcode, and can 

 be separated, theoretically at least, into an outer 

 transparent layer, termed the " ectosarc " or " ecto- 

 plasm," and an inner layer, granular and mobile, 

 called the " endosarc " or " endoplasm." It is the 

 outer layer which constructs the pseudopodia, while 

 the inner layer contains the nucleus, a spherical 

 vesicle which contracts and expands with something 

 approaching to regularity, and certain other cavities 

 of a temporary nature called vacuoles. These are the 

 only appearances of anything like organs that can be 

 detected, and there are no traces whatever of nervous 

 structure. The animal reproduces itself in the beau- 

 tifully simple way of merely dividing itself into two. 



Now we will take from our gatherings a tiny bit 

 of the pond weed, of which there is a quantity lying 



