CHAPTER VII 



TUNICATES OR ASCIDIANS AND LANCELETS 



THROUGHOUT this work attention has been 

 directed to the various " links," creatures which, 

 while inadmissible to any of the well-defined 

 groups, combine the characteristics of several and point 

 to a systematic development of life in an ever ascending 

 scale. To the casual observer the gulf between the 

 invertebrates — the creatures just reviewed — and the back- 

 boned creatures such as the fish, birds or man, is altogether 

 unbridgable. But throughout the seas at all depths and 

 in every conceivable situation there abound a race of 

 animals which combine the characteristics of invertebrates 

 and vertebrates in an astonishing manner. The members 

 of this group — the Ascidians — suggest little of an animal 

 nature. Many are firmly encrusted or shapeless masses 

 of flesh, whilst some resemble plants. Yet all have 

 certain characters in common and pass through the same 

 strange metamorphosis before reaching the adult and 

 usually sedentary stage. 



One character apparent in them all is an outer envelope 

 or tubing, which gives the group one of its names, whilst 

 the ever popular title of Sea Squirt is derived from the 



creatures shrinking when touched and ejecting the sea 



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