98 PROTOZOA. 



aided by the bubbles of water which often enter with the 

 food-particles, that the " contractile vacuoles " help in excre- 

 tion, are certain facts, though few details are known in regard 

 to these or other functions. In some cases a digestive ferment 

 seems to have been detected, and uric acid is said to occur 

 as a waste-product. 



To stimuli such as light, heat, or chemical reagents, the 

 Protozoa respond in a manner which shows considerable 

 sensitiveness, but specially endowed parts, such as pigment- 

 spots, are rare. The Protozoa sometimes behave in a way 

 which suggests conscious effort and intelligence, but as 

 cut-off fragments also act with marvellous reasonableness, 

 and as the nucleus cannot be regarded as a brain, there 

 seems no reason to credit them with more than that 

 diffuse consciousness which is possibly co-extensive with 

 life. Verworn has decided, after much labour, that the 

 Protozoa do not exhibit what even the most sanguine could 

 call intelligence, but this is no reason why he or any other 

 evolutionist should doubt that they have in them the inde- 

 finable rudiments of thought. 



Structure. — The Protozoa are sometimes called " struc- 

 tureless," but they are only so relatively. For though they 

 have not stomachs, hearts, and kidneys, as Ehrenberg sup- 

 posed, they are not like drops of white of egg. Our eyes, 

 when aided by the microscope, can distinguish structure in 

 these simplest animals. They are simple as an egg is simple 

 when compared with a bird. 



In some cases — probably in all — the cell-substance con- 

 sists of a living network or foam, in the meshes or vacuoles 

 of which there is looser material. Included with the latter 

 are granules, some of which are food-fragments in process of 

 digestion, or waste-products in process of excretion. 



The cell-substance includes a nucleus or several nuclei, 

 essential to the life and multiplication of the unit. There is 

 no need to preserve the term "Monera," applied to very simple 

 Protozoa supposed to be without nuclei, for in some of 

 these the nuclei have been discovered, and it is very probable 

 that nuclear material in some form exists in them all. The 

 nucleus is complex like the cell-substance, for where it is 

 large enough to be well observed, it is seen to consist of a 

 nuclear network, or a coil of nuclear threads. In the division 



