REPORT ON THE TUNIC AT A. 
39 
show how a complicated system might be produced by a series of gradual changes 
from the simple stellate system of a Botryllus. They are all for ms which are frequently 
seen in examining a number of colonies of different ages of a common Botrylloides {e.g., 
Botrylloides rubriim, IMilne-Edwards). 
A shows a system like that characteristic of Botrijllus and Polymjclus, composed of 
a few Ascidiozooids arranged radially around a circular common cloaca, so as to produce 
A SU „ 
c 
X 
D. 
Fig. 8.— Diagrams showing how a simple circular system (A) may develop through (B) and (C) into the condition 
characteristic of the systems in the genus Botrylloides, such as (D) and (B). 
a stellate figure. In B the system has become elongated, the Ascidiozooids are more 
numerous, and the common cloaca is elliptical. This condition may sometimes be seen 
in species of Botryllus, and it is common in young colonies of Botrylloides. In C 
the system has become much larger and the number of Ascidiozooids is greatly 
increased. Each end of the formerly elliptical system has become enlarged, and one of 
them is commencing to fork or divide into two branches. D shows a still larger and 
