FISHES AND SEA-SQUIRTS. 291 



process, and place in a pool or dish. In a minute or two 

 the shapeless creature recovers sufficiently to stretch itself 

 out in the water, and show at one end two elongated tubes, 

 placed close together, of which the one shows eight, and the 

 other six, red pigment spots close to the fringed openings, 

 which are of yellowish colour. The creature has a soft, 

 greenish coat, sufficiently translucent to allow one to see 

 through it the distinct muscle bands of the underlying 

 body-wall. By means of these bands it can retract its 

 tubes or siphons, and contract the whole body suddenly on 

 an alarm, the test, or coat, being so soft as to offer no 

 hindrance to the process. In this respect, Giona intestinalis, 

 as this particular Tunicate is called, differs from most of 

 its allies, which have generally such stiff coats that their 

 activities are limited to that sudden ejection of water which 

 gives them their common name of sea-squirts. When not 

 alarmed, Giona lies passively at the bottom of the dish, and 

 it can be seen that a continuous flow of water passes in by 

 the one siphon and out by the other. With a little care 

 the internal anatomy can be made out, the Tunicates being 

 usually fascinating creatures to dissect. As an aid in the 

 process, a figure is given of a Tunicate from fairly deep 

 water, in which the coat and tissues are so transparent that 

 the internal anatomy can be made out without dissection. 



Any Tunicate has outside the body the coat, or test (t), 

 made of a substance apparently identical with plant cellu- 

 lose, and varying greatly in thickness, colour, and con- 

 sistency. It can be very readily peeled off to show the 

 animal within. This has a thin muscular body-wall, usually 

 traversed by a network of slender muscular fibres, which in 

 Giona are collected in definite bands. The body has no 

 definite shape ; in Giona it is elongated, varying in length 

 from about two to five inches, but it is often rounded or 

 quadrilateral. In Giona the two apertures already noticed 

 are near together, and between them there is a little yellow 

 mass with a few radiating threads. This is all that repre- 

 sents the nervous system so small and undeveloped that 

 one can have few scruples about hurting a sea-squirt's 

 feelings ! It is hardly probable that it can ever suffer from 

 " nerves." 



Whatever the shape of the body in a Tunicate, tho 



