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TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



TUNICATA. 



(Fig. XXV.). 



The Ascidians, or sea-squirts, are not so well known 

 to the public as they deserve to be. They are very 

 common, very varied, and some of them very beautiful. 

 Most of them when adult stick to stones or sea-weeds, and 

 they are of two kinds — the Simple Ascidians and the 

 Compound Ascidians. A Simple Ascidian, such as Ascidia 

 (fig. XXY. 1), is a grey sack-like body from 1 to 6 

 inches in length, having a tough skin (the " Tunic," hence 



Pig. XXV. — Tunicata (natural size.) 



Tunicata) and two openings through one of which the sea- 

 water is drawn in, while it is squirted out through the 

 other. When touched incautiously, the animal contracts 

 and emits sudden jets of sea-water from both apertures, 

 thus vindicating its title to the popular name "sea-squirt." 

 The name Ascidian (from the Greek " Ascos," a leathern 

 double-necked bottle) is given in reference to the bag-like 

 shape and the two apertures. There are many interesting 

 and some puzzling points in connection with the structure 



