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 gangliop 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 Boliolum, 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- 



