THE ANATOMY OF A SEA SQUIRT 279 



rectified spirits of wine, shows (see Fig. 32) that it has a 

 complicated " anatomy." At the end of the sac opposite 

 to that by which it is attached in life to stones or weeds 

 one detects the animal's mouth, provided with a fringe of 

 very small tentacles. The mouth leads into a large flat- 

 tened chamber, extending through three fourths of the sac. 

 Its wall looks like a piece of gauze, perforated with rows 

 of innumerable fine holes. This is the enlarged gullet of 

 the Ascidian, and the sea-water which enters the mouth 

 is forced by the lashing of microscopic whips (called 

 " cilia ") to stream through the fine holes which they 

 fringe into an equally large flattened chamber lying over 

 the gullet. This second chamber is provided on one side 

 (not far from the mouth) with an upstanding opening 

 leading through the tough body wall or sac to the exterior. 

 This is " the peri-branchial chamber," so called because the 

 perforated wall of the gullet has fine blood-vessels run- 

 ning along its meshes, and acts as a gill or branchial breath- 

 ing apparatus. The water streaming into the mouth and 

 through the meshes of the gullet wall into this chamber, 

 and by its " pore " or orifice to the exterior, oxygenates 

 the blood as it courses along the bars of the network. 



The solid particles of a nutritious nature (often micro- 

 scopic plants and animalcules) which enter with the water 

 into the gullet are strained off by its sieve-like wall, and 

 pass at its lower end into the coiling intestine, which is 

 visible when one first roughly opens an Ascidian. The 

 intestine does not open to the exterior, but after forming a 

 loop turns on itself and opens into the peri-branchial cham- 

 ber, so that the current of water passing through that cavity 

 carries away the matter discharged from the intestine 

 through the branchial pore to the exterior. Thus the 

 Ascidian is provided with an elaborate apparatus which 

 makes one continual stream of water drawn into its mouth 

 serve as a carrier of food particles to the digestive gut, of 



