BOTKYLLIDJE. 31 



Authorities. I have been chiefly indebted to 

 M. Savigny's "Memoires sur les Animaux sans Ver- 

 tebres;" Dr. Milne-Edwards' s " Observations sur 

 les Ascidies Composees ;" Messrs. Forbes and Han- 

 ley's " British Mollusca;" Siebold and Kolliker's 

 " Anatomy of the Invertebrata " (Burnett's edi- 

 tion) ; and Professor Huxley's " Memoir on Salpa 

 and Pyrosoma." 



TUNICATA. 



Molluscous animals enveloped in a test composed 

 of cellulose, furnished with two orifices, a receiving 

 (branchial) and a discharging (anal) one ; mantle 

 forming an interior tunic, also furnished with two 

 orifices corresponding with those of the test, and 

 adhering to them ; gills occupying the interior 

 surface of a membranous sac, hanging between the 

 branchial orifice and the entrance of the stomach, 

 and leading to the latter. 



Animal attached ; mantle united to the 

 test only at the orifices. 



Individuals organically united in 

 systems Botryllidte. 



Individuals distinct, but associated by 

 a common root-thread Clavelinadte. 



Individuals isolated ...... Ascidiada. 



Animal free ; test and mantle united 

 throughout. 



Orifices near together Pelonaada. 



Orifices placed at opposite extremities Salpada. 



FAMILY I. BOTRYLLID^. 



Aplidium (Sav.). Mass sessile, varying in form, 

 gelatinous, or cartilaginous, composed of numerous 

 systems, with no central cavity. Animals com- 



