STRUCTURE OF PROTOZOA 1 39 



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 hsemoglobin of the host. 



Psychical life. — Protozoa often behave in a way which 

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

 frag'ments 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 colloidal mixture, 

 often with vacuoles. In many cases there are numerous 

 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 : — 



(i) 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. 



(2) In the majority of cases, notably in, the Sporozoa, the nucleus 

 is single, often large, and placed centrally. From a consideration of the 

 cells of Metazoa we may call this the typical case. 



(3) In many of the Ciliata, e.g. Pararncecium, there are two dimorphic 

 nuclei. There is a large oblong nucleus, and beside it a smaller 

 spherical one. 



{4) In some Ciliata the macronucleus exists in the form of powder 

 scattered through the protoplasm, e.g. in Opalinopsis. The granules 

 may collect to form a compact nucleus when fission is about to take 

 place. 



