28 TUNICATA. 



find between tide-marks, adhering to sea-weeds or 

 to stones, of various gaj colours, set with minute 

 stars of brighter hues. These stars, or systems, of 

 which there may be many in a single patch, are 

 composed of minute Tunicata, set in a radiating 

 circle, and marked by this peculiarity ; that instead 

 of the two orifices being placed close together, as 

 usual, the receiving one alone is directed outwards, 

 the discharging one opening at the opposite extre- 

 mity into a common circular reservoir, which is 

 the outlet of that particular system. 



In other cases the animals are united into com- 

 pound systems, enveloped in a common mass ; but 

 the form of each animal is that already described, 

 each having its own discharging orifice placed near 

 the receiving one. These compound encrusting 

 forms show a relation to the Alcyonidiadce among 

 the POLYZOA. 



There are other genera, again, which consist of 

 animals individually distinct, and of the ordinary 

 structure, but which spring singly from a common 

 creeping root-thread. These [Clavelinadoi) present 

 the most close analogy with the condition of the 

 Vesicidainadce^ and particularly of Pedicellina. 



Though the general habit of this Class is to be 

 permanently fixed to foreign bodies, yet there are 

 some members of it which are free. The genus 

 PeloncRa appears to have a form, structure, and 

 habits, which bring it into proximity with some 

 of the worm-like Echinodermata. " They pre- 

 sent the remarkable positive anatomical character 

 of an union of mantle with test^ * 



In this latter character they are paralleled by 

 the still more free Salpadce, creatures which difi'er 



* Forbes and Hanley ; Br. Moll. i. 42. 



