4.58 FREDERICK KEEBLE. 
weed from the Paradoxa zone was added, and on the following 
day infection was observed. The results of this experiment 
are summarised in Table I (Infection Record), where it will 
be seen that, of 14 animals examined, 8 showed no sign of 
infection, and 6 showed infection in various stages: from the 
stage in which one yellow-brown algal cell was present in the 
animal to that in which large numbers of yellow-brown cells 
occurred, ‘This was one of the most successful of the many 
infection-experiments which were carried on in 1906 and 
1907. In others the proportion of infected to uninfected 
animals was smaller, and in some cases no infection was 
obtained. From this it is to be concluded that the changed 
conditions in the laboratory affect the infecting organism 
adversely or that its distribution in the weed is sporadic, 
Yet another possibility must not be lost sight of, namely, 
that under some circumstances, e. g. when the conditions, 
as, for example, those obtaining in the laboratory, are some- 
what unfavourable, the yellow-brown cells taken up by the 
larvee may suffer digestion just as was shown to be the case 
with the yellow-brown cells of the adult. As indicative of 
the probability that this fate may overtake the infecting 
aleal cell, several records occur in the notes of infection 
experiments to the effect that a larva, exhibiting no normal 
yellow-brown cells, nevertheless contained digested rem- 
nants of such cells. The fact that in nature no C. paradoxa 
are to be met with which do not contain large numbers of 
yellow-brown cells is no argument against the probability of 
this view, since, under natural conditions, reinfection would 
doubtless occur. On the other hand, the conception that it 
is not a foregone conclusion that, once arrived in the body of 
C. paradoxa, the algal cell will grow and divide, contributes 
a little toward an understanding of the way in which the present 
relations between algal cell and animal may have originated. 
The animal, it may be conceived, plays with respect to the 
yellow-brown cells the part which that discriminating Provi- 
dence, Natural Selection, plays with respect to living things 
in general. Not all the entering algal cells pass its test; nor, 
