W. K. BROOKS ON THE GENUS SALPA. 189 



While it is not my purpose to discuss the ancestral history of the 

 vertebrates, the remote phylogeny of the tunicates is unquestionably 

 identical with that of the other chordata, and I cannot ignore the general 

 acceptance of an opinion which is absolutely irreconcilable with the one 

 which I have presented. 



This prevailing opinion has interwoven itself with the literature in 

 such a complicated way that one may well shrink from the interminable 

 labor which the critical revision of the whole of it would involve. I 

 myself decline to undertake what I regard as an unprofitable and useless 

 task ; unprofitable, as the literature rests on an untenable and false basis, 

 and useless, since I do not hope to induce those who have stored their 

 minds with the endless details of morphology docketed and pigeon- 

 holded according to a false system, to unload all this rubbish and to 

 build again on a new foundation. 



I shall therefore restrict myself to a discussion of the origin of the 

 two most characteristic systems of tunicata organs, the gill-slits, and the 

 pharyngeal ciliated cells and gland cells; and I shall here confine myself 

 to the observations and reflections of a single writer, Dr. Dohrn. 



I make this selection the more willingly, as Dohrn's name is most 

 intimately associated with the annelidian hypothesis, and because his 

 writings are not only the ones which have been most influential, but also 

 the ones which are most comprehensive and most attractive to the reader. 



The "Ursprung der Wirbelthiere " is a most fascinating book. Soon 

 after it appeared I placed it in the list of works which my students are 

 advised to read, and for many years an acquaintance with it has been 

 expected of all who have been examined for the degree of Ph. D. in the 

 Johns Hopkins University. 



My students have even prepared for their own use an English trans- 

 lation of it, and I have read it with them several times with interest and 

 pleasure. At the first reading my pleasure was almost that of convic- 

 tion, but as the ingenious details became familiar, and the essay was 

 more sharply focused in its completeness, and was held, as it were, at 

 arm's length, so that the whole picture could be seen at one view, I have 

 read it, as I have read Gulliver's Travels, with admiration for the skill 

 which has elaborated it in such logical minuteness from a fundamental 

 assumption which is purely imaginary. 



The story, as told by Dohrn in the "Ursprung," is so consistent and 

 logical that I see no reason why animals like the tunicates might not 

 have been evolved in the way which he pictures so vividly, although I 



