114 PHYLUM PROTOZOA THE SIMPLEST ANIMALS. 



also symbiotic Algae, which have lost the power of independent exist- 

 ence. The evidence for this is, however, insufficient, and this explana- 

 tion will not apply in cases like that of Vorticella viridis, where the 

 freen colouring matter is uniformly distributed through the protoplasm, 

 n many cases there is, besides the chlorophyll, a brown pigment, 

 identical with the diatomin of Diatoms. In many of the Flagellata 

 there are one or more bright pigment spots at the anterior end of the 

 cell ; these may be specially sensitive areas. In some of the simpler 

 Gregarines the medullary protoplasm is coloured with pigment which is 

 apparently a derivative of the haemoglobin of the host. 



Psychical life. Protozoa often behave in a way which 

 suggests control, but it should be noted that cut-off 

 fragments sometimes behave just as effectively as the 

 intact units. Verworn has decided, after much labour, 

 that the Protozoa do not exhibit what even the most 

 generous could call intelligence ; but this is no reason why 

 he or any other evolutionist should doubt that they have in 

 them the indefinable rudiments of mind. Jennings has 

 shown that the behaviour of some Infusorians corresponds 

 to what may be called the method of trial and error ; they 

 "try" one kind of response after another until, in some 

 cases, they give the effective answer. 



GENERAL NOTES ON THE STRUCTURE OF PROTOZOA 



The Protozoa are sometimes called "structureless," but 

 they are only so relatively. For though they have not 

 stomachs, hearts, and kidneys, as Ehrenberg supposed, they 

 are not like drops of white of egg. 



The cell substance consists 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 one or more nuclei, special- 

 ised bodies which are essential to the life and multiplication 

 of the unit. In the Protozoa there are several conditions 

 under which the nucleus may exist : 



(l) In some adult forms, and in many spores or young forms, no 

 definite nucleus has yet been discovered. It is, however, unnecessary 

 to preserve the term " Monera" for such simple forms, as it is probable 

 that nuclear material does exist in the form of granules. 



