136 THE STORY OF ANIMAL LIFE 



great discovery belongs to Russia ; for the pres- 

 ence of the Notochord in the Ascidian larva was 

 discovered by A. Kowalevsky, in 1866. 



To the present generation of zoological stu- 

 dents, the Chordate affinities of Ascidians are part 

 of the A B C of knowledge ; and it is hardly pos- 

 sible for them to realise that it is only thirty 

 years ago since the idea was so new that Huxley, 

 in his "Text-book of the Vertebrata," only al- 

 luded to it in a footnote. Would-be zoological 

 critics, at a somewhat later period, met the theory 

 with ridicule, for want of better argument. For 

 critics include not only "those who have failed in 

 literature and art," but also those who have failed 

 in science. 



The majority of the Ascidians are sessile ani- 

 mals, which fix themselves, like Sea- Anemones, 

 to some object when they have passed their earli- 

 est stages of growth ; and although there are 

 many forms that swim freely, most authorities 

 are inclined to believe that these have arisen by 

 adaptation, and that the kinds that are fixed when 

 adult are the original type of the group. 



Anything more unlike what we should expect 

 to find as a relative of the vertebrates could not 

 possibly be imagined. What has been written 

 about these little animals by various observers 

 would make a whole series of volumes of the 

 size of this one, so many are the puzzles afforded 

 by their internal structure. The arrangement of 

 their organs is in many respects very unsym- 

 metrical. Their most striking peculiarity, per- 

 haps, is the nature of the gills. These form a 

 kind of basket-work, consisting of minute holes 

 with intermediate supports; and they are asso- 

 ciated with a special cavity outside them called 



