320 
THE VOYAGE OF H.M.S. CHALLEHGEE. 
Ascidiozooids open independently. It is evident that although the form of the colony in 
the present species closely resembles that of Pyrosoma, still the inner surface lining the 
central cavity is homologous with part of the outer surface of the ordinary Compound 
Ascidian and not with the inner surface lining the central cavity of Pyrosoma. The 
present species is therefore to be regarded as an unattached Compound Ascidian, which 
shows, in the peculiar form of its colony, a transition to Pyrosoma. 
The central cavity in Coelocormus Tiuxleyi divides about the middle of the colony into 
two branches which end csecally and are separated from one another by a rounded 
eminence (see fig. 10, B, and PI. XXXVIII. fig. 1) bearing on its summit a large irregu- 
larly rounded opening. This is the only common cloacal aperture visible in the specimen. 
The Ascidiozooids are rather smaller and more numerous near the open end of the 
A B 
Fig. 10. — Diagrams showing the relations between — A, a typical Compound Ascidian ; B, Codoconreus ; C, Pyrosoma. In all 
cases the colonies are represented in longitudinal section, and cl. indicates the opening of the common cloacal cavity. 
colony than elsewhere. They are of large size and are fairly abundant about the 
centre, while at the closed end they are almost absent (PL XXXVII. figs. 1, 2), that 
part of the colony being mainly a mass of solid test in which some very large tailed 
larvse are found imbedded. Probably the young Ascidiozooids are formed by gemmation 
at the open end, which is thus the growing point of the colony, and gradually 
move farther and farther away from the common cloaca, which may be regarded 
as the oldest part of the colony. The older and larger Ascidiozooids, as they approach 
the rounded closed end, probably die and are expelled from the colony, leaving behind 
them, imbedded in the test, the embryos or larvse which they have produced during 
the later part of their existence. If this interpretation of the life-history of the 
colony is correct, the Ascidiozooids reproduce by gemmation during the early part of 
their existence, and sexually later on, when they are adult. 
