72 MICROSCOPICAL STUDIES, rr . 



and so have deserted the free-swimming life evidence being that 

 the fixed Ascidians recapitulate very closely, in their larval condition ^ 

 the general form, together with many of the essentially characteristic 

 internal features of adult Appendicularians. But the student not 

 thoroughly on his guard against the pitfalls of evolutionary reasoning, 

 might easily deduce that the Appendicularians are arrested larvas 

 of fixed Ascidians ; that is, that certain larvae instead of performing 

 the full life-history of their race, retained the tailed form all their 

 adult life, and that the occasional formation of the " haus " is the 

 atavistic recollection of the fixed Ascidian condition ! ! 



In reality such conclusion is easily refuted, and there is really 

 no reasonable doubt that the tadpole larvas show the ancestral form 

 fairly clearly. To mention one argument only, why should they have 

 a nervous system infinitely superior to that of the adult, formed too 

 on a plan entirely different from any to be found among inver- 

 tebrates, but characteristic of vertebrates ? 



Correction. On page 8, line 6, read "ovary" instead of "ovum. 



