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young sea squirt fixes itself to some object by the 

 suckers with which its head extremity is provided. 

 The tail begins to shrivel, whilst the body enlarges 

 and the throat increases in size. Then the atrium 

 and the leathery skin are formed, and finally the 

 animal becomes the bag-like organism with which we 

 started. As a sea squirt, pure and simple, the animal 

 loses all, or nearly all, the characters by which it was 

 related to the lancelet ; and but for the knowledge of 

 what it ivas, we should therefore hardly know what a 

 sea squirt (or indeed, any other animal) really is. 



What, now, are the legitimate inferences to be 

 drawn from the facts above detailed, and which, it 

 may be remarked, are the common details of modern 

 zoological instruction ? Firstly, that, whilst the lancelet 

 is the lowest Vertebrate, it shows its affinities to other 

 vertebrates clearly enough in the possession of a 

 notochord and of the other characters already detailed. 

 Secondly, that the sea squirts are the only animals 

 which present any likeness to the lancelet, and through 

 it to other vertebrates man included. Thirdly, that 

 this likeness is so real and so close in all respects that 

 the affinities of the two groups cannot be doubted. 

 The likeness is seen not only in the possession of a 

 notochord found in no other Invertebrated animals 

 but in the curious throat with its gill-slits, and in the 

 nervous axis placed above the notochord. Again, the 

 likeness in the earliest stages of development is still 

 more startling ; the egg of the lancelet and that of 

 the sea squirt develop in precisely similar fashion. 



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