448 ZOOLOGY 
a long tail which is attached ventrally to the body and is bent 
forward. The mouth leads straight into the branchial sac, 
which opens directly to the exterior by two ciliated apertures ; 
there is no atrial chamber. The hypopharyngeal groove is 
short, and there is no dorsal lamina. There is an oesophagus 
stomach and intestine which ends in the anus situated just in 
front of the ciliated pores. The main nervous ganglion is in 
connection with an otocyst and a pigment spot or eye, it gives 
off posteriorly a nerve cord, which passes by the side of the 
alimentary canal into the tail and then runs along the left 
side of the notochord. In the tail the nervous axis enlarges 
into several ganglia, which give off nerves to the surrounding 
parts. The notochord is confined to the tail, and the muscles 
in the same region are broken up into segmentally repeated 
bands. The heart is said to be composed of two cells. The 
testes and ovaries are at the posterior end of the body, and 
open directly to the exterior. 
Appendicularia, like the other members of the order, pos- 
sesses the power of secreting with extraordinary rapidity a 
temporary gelatinous covering or test, which corresponds with 
the test of Ciona. This test is, however, soon cast aside, but 
another one may be formed shortly afterwards. 
The Larvacea do not reproduce by budding, and their 
developement is direct. 
Order 2. THALIACEA. 
This order contains certain free-swimming forms, which in 
the adult state are not provided with a tail with notochord, 
etc. Some members of this order, as Doliolum, are single 
animals with a complicated alternation of generations in their 
life-history. The sexual form is hermaphrodite, and the ovum 
gives rise to tailed larvae which grow into asexual forms dif- 
fering slightly from the sexual generation. These asexual 
forms reproduce by budding. The buds develope into the 
sexual generation, which is complicated by being polymorphic ; 
there being three forms, of which only one has functional 
generative organs. 
Other members of this group present still greater com- 
