1884.] Colonial Organisms. 143 
an interesting subject to which some further attention is desirable. 
As already said, each developing cell to a certain extent exhausts 
the organism and checks the reproductive activity of other cells. 
What is the principle of selection of these fortunate cells? It 
would seem as if they must possess Superiority in nutrition, or 
be most favorably situated for assimilating nutriment from the 
vascular juices of the organism. Thus growing rich in proto- 
plasm, their effort to develop must be not too greatly hampered 
by the crowding of surrounding cells. They must have some 
freedom of field in which to expand. The cell most favored in 
these particulars will be the most likely to develop. As for the 
germ cell of sexual reproduction, it possesses these requisites in 
a high degree. It develops in a region which is richly supplied 
with nutriment, and where there is no hindrance to its expansion. 
Of the many cells delivered into this region it would seem that 
those richest in protoplasm should, all things considered, have 
the best chance to develop and become the germs of new organ- 
isms. In sexual development, however, there must enter a cer- 
tain element of chance, since the meeting of ova and spermato- 
zoa is, to some extent, a matter of chance, and the earliest fertil- 
ized ova probably have a degree of advantage over their rivals. 
With these preliminary remarks we may proceed to the con- 
deration of the colonizing habit as usually displayed by the 
Products of asexual generation. Colonial organisms occur abun- 
_ dantly in the single-celled field of life, as in the Diatomacez, the 
Volvocineæ, the Foraminifera, the Radiolaria, the Flagellata, &c. 
In the multicelled field it is indicated throughout the vegetable 
ngdom, and in the Spongida, the Hydrozoa, the Actinozoa, the 
P olyzoa, the Ascidia, the Annelida and the Arthropoda of the 
Ammal kingdom. But these indications of colonial origin are by 
— means all equally distinct, and in some of the sub-kingdoms 
Mentioned they are but vaguely discernible. Yet there is a grad- 
ual movement from the less to the more questionable colonies 
: which is significant of a common origin, 
i ose colonies of Rhizopod and Flagellate Protozoa no traces 
| €rentiation appear. Each individual is like all the others, 
each is capable of separate existence. We cannot, in any 
i Sense, consider these colonies as compound individuals, 
though in the Foraminifera there is a slight tendency in that 
Sirection This tendency is more markedly displayed in the 
S 
