MOLLUSCA. 



173 



Appendiculariidae [ = " suborder Copelatse "] appear to retain 

 a tadpole-like larval form through life. Of Appendicularia 

 flagettum, Huxley says it has " an ovoid or flask-like body, one 

 sixth to one fourth of an inch m length, to which is attached a 

 long curved lanceolate appendage or tail, by whose powerful 

 vibratory motions it is rapidly propelled through the water." 

 It has the power of excreting from the surface, " with extreme 

 rapidity, a mucilaginous cuticular investment, in the interior of 

 which, as in a spacious case, the whole body is lodged." 



The two British species of Pelonaiidse are found in the mud in 

 deep water ; they are not fixed, and their outer and inner integu- 

 ments are united. According to Goodsir and Forbes, " they 

 indicate a relation to the cirrhograde Echinodermata." Clavel- 

 linidae are social, connected by creeping prolongations of a common 

 stem, and having a common circulation. Botryllidae are com- 

 pound, each individual imbedded in a jelly-like substance ; and 

 Aseidiidae are simple forms, always fixed. Hypobythius occurs at 

 a depth of l!900 fathoms. 



Pyrosomatidae [ = " suborder Lucise"] are free-swimming aggre- 

 gations of individuals united together in the form of a hollow 

 cylinder, sometimes 14 inches long, one end of each individual 

 opening into the cavity of the cylinder. They are highly 

 luminous, two phosphorescent organs being found in each indi- 

 vidual ; they are pelagic, and seem merely to float about in the 

 water. 



Cynthia. 

 Styela. 



Clavellina. 

 Perophora. 



Pyrosomatidce. 

 Pyrosoma. 



