RELATIONSHIPS OF THE FIXED AND FREE TUNICATA. 177 



Table of Classification — continued. 



2. Gemmae springing separately from a definite " ascidiarium (J^wa;.), and communicating 



indirectly through a central common vascular system, . Social Tunicata. 



A. Zooids branchial {Hux.'), pedunculated, springing from a scandent or Genera. 



repent corneous axis, with a central permanent vascular system 



common to the offsets, ....... Perophora. 



B. Zooids intestinal [Hux.) 



1. Pedunculated. 



a. Standing upon a repent ramose cartilaginous case, with a 



central canal (usually not permanent), communicating with 



the offsets, ........ Clavellina. 



b. Developed centripetally on an erect, simple, cylindrical stem, 



permeated by numerous longitudinal canals communicating 



with the offsets, though rarely with each other, . Chondrostachys. 



2. Sessile, clustered in irregular circles on a simple depressed axis, Syntethys. 



And, probably, ........ C?) Diazona. 



3 . Gemmae arising separately from the parent, with or without vascular inter- 



communication, but always immersed in a common test or "ascidi- 

 arium," .......... Compound Tunicata. 



A. Pallio-vascular system simple, i.e., not intercommunicating. Genera. 



1. Excretory aperture opening directly upon the surface. Cloacce o. 



a. Biabdominal (Polyclinian). Zooids in irregular circles, one 



above another, ....... Sigillina. 



b. Abdominal (Didemnian). 



1. Zooids in one or two rows at unequal distances from 



centres, ....... Distomus. 



2. Zooids without distinct circumscription. 



a. Abdominal viscera beside the thorax, . Euccelium. 



b. Abdomen pedunculate, . . . Didemnium. 



2. Excretory aperture opening into a common cloacal system. 



a. Cloaca superficial reticulate, with tributary canals diverging 

 from the zooids in the intervening spaces. 



a. Thorax double, ...... Diplosoma. 



b. Thorax simple, ...... Leptoclinum. 



b. Cloacae deeply excavated, dendritic, formed by the con- 

 fluence of converging canals. 



1. Biabdominal (Polyclinian), 



a. Systems diffuse. 

 a. Branchial aperture 6-rayed, . . Amarcecium. 

 jS. Branchial aperture 8-rayed, . . Parascidium. 



b. Systems circumscribed. 

 . Without central cavities, . . . Aplydium. 

 . With central cavities, . . . Polyclinum. 



