96 JOHN BEARD. 
lateral nerve-cords were supposed to have coalesced dorsally 
instead of ventrally, as in Annelida. 
Following this one is reminded of Hubrecht’s theory, which 
allies Vertebrates with Nemertines, and sees the Vertebrate 
notochord reflected in the Nemertine proboscis sheath. 
By no means least important is the celebrated Annelidan 
theory of the origin of Vertebrates first originated by Dohrn! 
and Semper.? A theory which, in spite of all attacks, still 
survives, and at present seems to be more probable than any 
other. 
Finally, the alliance of Balanoglossus with Ascidians, Amphi- 
oxus, and Vertebrates, recently advocated by Bateson,? must be 
mentioned. Interesting though this is, it cannot yet be consi- 
dered as sufficiently established to be accepted without reserve ; 
but if more evidence for it be forthcoming it is a moot point 
whether our existing notions of the relations of Vertebrates 
and Annelida will not have to be modified, for we know of no 
existing Annelid which has relationships with Balanoglossus. 
And here I would point out that my own researches on the 
cranial nervous system and sense organs of Vertebrates, instead 
of supporting the alliance of Balanoglossus with Vertebrates as 
high as fishes, present rather a hindrance in the way of such 
alliance, whilst they are still more opposed to the alliance of 
Vertebrates with existing Annelida. 
That Vertebrates have their nearest allies, except Balano- 
glossus, in the group of Annelida, is becoming more and more 
obvious from recent researches, especially from those of Dohrn ; 
but the links of such an alliance seem to have been rather in 
long extinct Annelida than in any at present existing. 
In the following pages an account will be given of the mor- 
phology and development of the branchial sense organs and 
associated ganglia in Amphibians and Fishes, chiefly in Elas- 
1 Dohrn, ‘Ursprung der Wirbelthiere,’ 1875. 
2 Semper, “‘ Verwandschaftsbeziehungen der gegliederten Thiere,” ‘ Arbei- 
ten a. d. Zool. Institut zu Wiirzburg,’ 1875. 
8 Bateson, W., ‘‘ Development of Balanoglossus,” ‘Quart. Journ. Micro. 
Sci.,’ Supplement, July, 1885. 
