THE SEA-SQUIRT'S COAT 281 



also a minute brain, a knob the size of a large pin's head, 

 consisting of nerve-cells, from which pass nerve-fibres to 

 the muscles, and also to certain organs of touch and 

 taste. The thick translucent sac, which forms the coat of 

 our Ascidian, is a complete closed sac, except for the two 

 holes not far from one another, where the mouth and the 

 orifice of the branchial chamber respectively open (see 

 F'g- 31)' This coat or sac is one of the most peculiar 



Fig. 33._Brilliantly coloured star-like growths united by a common 

 dense jelly so as to form a mat, which adheres to a piece of brown sea- 

 weed. This is the compound Ascidian called Botryllus. Each star 

 consists of eight or nine little creatures like the Ascidian of Fig. 32, 

 but they are united side by side to one another and have one 

 common aperture (seen as a black dot in the centre of each star) 

 for their peri-branchial chambers. Each of the constituent indi- 

 viduals of a star has its own mouth near the edge of the circle. 

 The drawing is of the natural size. 



and characteristic structures of all the varied kinds of 

 Ascidians. They have, in reference to it, received the 

 name " Tunicata." It consists of a dense, more or less 

 transparent deposit, in some kinds as hard as horn and a 



