254 M. M. Mercaur 
of the fact of a chemical and physiological difference between the 
ectosare and endosare, leaving unexplained the nature of this difference. 
Excretory organs. 
The special connection of the excretory organs with the nuclei 
is worth emphasis, though just what its physiological meaning may be 
is unexplained. . 
It is also of interest that the granules massed in the posterior 
end of the system of excretory vacuoles, which are from time to time 
extruded from the body, seem to be derived from granules of the 
cytoplasm, as indicated by their size and their exact resemblance 
to the granules of the cytoplasm bounding the posterior vacuole of 
the excretory system. In the processes of excretion certain of the 
cytoplasmic granules seem to be thrown away bodily. 
The very primitive character of the excretory organs in Opalina 
has been emphasized in a previsious paper (Mrercaur 1907 c). 
Anterior end of the body. 
The divergent character of the anterior end of the body also 
deserves special note. One sees that in this region the granules of the 
endosarc are more numerous, and the endosarc spherules much more 
abundant (Fig. 1), while in the ectosare the very large alveoli and 
the large ectosarc spherules are wanting. As division of the body is 
constantly going on, growth must be constant, and one naturally thinks 
that the denser character of the anterior end may be related to 
special activity in this growth, yet this is not easy to prove. There 
are no definite points in the body which can be taken as landmarks 
in estimating the relative growth of different regions. The nuclei 
move within the plasma and so cannot be used as a fixed point for 
reference in studying the relative growth of different regions. That 
they so move is shown by the fact that one daughter cell, in each 
division, receives the posterior nucleus from the parent and that in 
a short time this comes to lie as near, or almost as near, to the 
anterior end of the body as does the nucleus in the other daughter 
cell (Pl. XVII). 
Absence of centrosomes. 
The absence of centrosomes in the mitosis is of interest. Centro- 
somes are well known among the Protozoa (e. g. in the Sporozoa). 
Among Flageilata and Foraminifera and in certain Ciliata, structures 
