ZOOPHTTES, 27 



Order TV.— ASCIDIOIDA. 



There is among the moUnscous or soft -bodied animals, which 

 in popular language are known as "shell-fish," a numerous 

 order in which the animals are covered, not -with calcareous 

 shells, but with a soft membranous covering or tunic, and 

 are hence called tuuicated mollusca. Among them is a genus 

 bearing the name of " Ascidia," one species of which is 

 everywhere abundant round our coast. To this the Zoophytes 

 of the present order bear such resemblance in structure, tl;at 

 the name "Ascidioida" is employed to denote the likeness.* 



Fig. id. — I'lCMATKLLA a, natunil size. — b, a group, magni£eJ. 



These Polypes are not separated, but aggi'egated; their 

 polypidoms are very variable, both in form and in material; 

 sometimes enamelling mth delicate net-work the fiond of a 

 seaweed or the exterior of a bivalve shell, at others rising 

 into the asp(^ct of miniature plants, or broad leaf-like expansions. 

 They are furnished with distinct orifice^ for the reception of 

 food, and for throwing off its undigested remains {Fig. 15). 

 Round the mouth is a circle of retractile tentacula covered with 



* May, i8'J4. Becent Investiijati Dns have shown that this is not a mere 

 leseiubiance, l)ut a real affinity — that they are formed on the true molluscan 

 type, and slioulJ \>i placed with the MoUusca Tunicalcu 



