NOTES ON THE STRUCTURE OF PROTOZOA. in 



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 areas which are essential to the life and multiplication 

 of the unit. In the Protozoa there are several conditions 

 under which the nucleus may exist : 



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

 nucleus has yet been discovered. It is, however, unnecessary to pre- 

 serve the term " Monera " for such simple forms, as it is probable that 

 nuclear material does exist in some form even in these cases. 



(2) In some of the Ciliata the nucleus is diffuse, that is, it exists in the 

 form of a powder scattered through the medullary protoplasm, and is 

 only discernible after death by means of careful staining. In Opalin- 

 opsis the fine powder sometimes coalesces into a single nucleus. 



(3) 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. 



(4) In many of the Ciliata, e.g. raramcecinm, there are two dimorphic 

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

 spherical one. 



(5) In Opalina, from the intestine of the frog, and a few other forms, 



