ON PHORONIS OVAL1S, STRETHILL WRIGHT. 
135 
already recorded, that the process of fission may be repeated 
several times in one original individual and its products. 
The tube A-K appears to be part of a tube originally 
inhabited by a single individual, and added to from time to 
time as the result of successive transverse fissions of its 
inhabitants. A is the proximal end, and K the distal end 
of the portion represented. The transverse septa at B , 
F, and I, may be taken as indications of as many transverse 
fissions The segment of the tube between B and F has 
been occupied by an individual which has formed a new 
distal end to its tube at G-, and has restricted the size of the 
rest of its tube by the formation of the irregular, longitudinal, 
secondary deposit of tube-substance seen at L. The septum 
H may indicate merely a part of this process of reducing the 
size of the tube, but fission may have occurred at this point, 
in which case it must be assumed that the segment of the 
animal which occupied the portion B-H had not succeeded 
in forming a new distal end to its tube. The portion of tube 
situated proxitnally to the septum I has grown out into the 
irregular tube J. On the proximal side of the septum B a 
considerable length of the distal part of a tube has been 
formed at C. This individual occupied only a short portion 
of the original tube, a septum having been formed at M; 
and it then appears to have grown out proximally, in the 
direction P, a further fission of the inhabitant of the tube 
being indicated by the septa E. It is not impossible that the 
fragment of the individual left in P may have turned com- 
pletely round in its tube, so that E became the proximal end 
and P the distal end of its tube, but of this there is no 
evidence. 
The appearances presented by this system of tubes, 
together with the evidence brought forward in the next 
section ( d ) suggest that fission occurs repeatedly in this 
species, and it seems not improbable that all the numerous 
individuals found in a given area of the shell may have been 
derived by fission from a single metamorphosed larva, or 
from a small number of individual larvae which succeeded in 
