Ascidians 57 



settle clown into adult life, the Appendicularice are 

 Ascidians which retain tliis larval structure throughout 

 life. Von Baer had shown that in the great natural 

 groups of higher animals some forms occur which 

 typify, in their adult condition, the larval state of the 

 higher forms of the group. Thus, among the amphibia, 

 frogs have tails in the larval or tadpole condition ; but 

 newts throughout life remain in the larval or tailed 

 condition. Appendicularia he considered to be the 

 lowest form of the Ascidians, and to typify in its adult 

 condition the larval stages of the higher Ascidians. 



By this remarkable investigation of the structure of 

 the group of Ascidians, and display of the various 

 grades of organisation, Huxley paved the way for one of 

 the great modern advances in knowledge. When, later 

 on, the idea of evolution was accepted, and zoologists 

 began hunting out the pedigree of the back-boned ani- 

 mals, it was discovered that Ascidians were modern 

 representatives of an important stage in the ancestry 

 of vertebrate animals, and, therefore, of man himself. 

 There are few more interesting chapters in genealogical 

 zoology than those which reveal the relationship be- 

 tween Amphioxus and fish on the one hand, and 

 Ascidians on the other ; for fish are vertebrates, and 

 Ascidians, on the old view, are lowly invertebrates. 

 The details of these relationships have been made 

 known to us by the brilliant investigations of several 

 Germans, by Kowalevsky, a Russian, by the English- 

 men Ray I^ankester and Willey, and by several 

 Americans and Frenchmen. But behind the work of 

 all these lies the pioneer work of Huxley, who first 

 gathered the group of Ascidians together, and in a 

 series of masterly investigations described its typical 

 structure. 



