192 Balanoglossits. [zoe 



in the form of a pouch extenduig through the peduncle somewhat 

 into the base of the proboscis. Its connection with the digestive tube 

 never becomes severed as it does in all vertebrates. 



It appears to me that it is in the "branchial basket" and the 

 parts immediately associated with it that we find the most convinc- 

 ing evidence of genetic relationship between Balanoglossus and ver- 

 tebrates. In this particular greater similarity exists between Bala- 

 noglossus and Amphioxus, than between the Cyclostome fishes and 

 higher fishes. And the resemblance is the more convincing because 

 of the complexity of structure— the large number of points pre- 

 sented for comparison in the two cases. A detailed description and 

 comparison of all these points is quite out of the question in the 

 present connection. I may mention some of them, however, and 

 refer those who may desire to examine the subject more carefully 

 to the papers of Agassiz,® Spengel," Bateson,^ Lankester,® Morgan,^" 

 Willey," and others. These are: the method of origin of the 

 primary gill slits in the two cases, and the way in which these 

 are each divided into two in later life by the so-called tongue bars; 

 the very large and somewhat variable number of gill slits, as com- 

 pared with all vertebrates, and the fact that the number in- 

 creases till a late period in the developmental history of the ani- 

 mal; the similarity of the chitinoid bars that serve as a framework 

 for the gill slits in the two cases; the beginning, so to speak, in 

 Balanoglossus, of what would correspond, both in origin and in 

 morphological relations, were the development carried further, to 

 the atrium of Amphioxus; and finally, but by no means least in 

 possible significance, the collar funnels in Balanoglossus comparable 

 to the atrio-coelomic funnels in Amphioxus. These latter structures 



* Alexander Agassiz. The History of Balanoglossus and Tornaria. Mem. 

 Amer. Acad. Arts and Sci., Vol. ix, 1867. 



'J. W. Spengel. Ueber den IJau und der Entwicklung des Balanoglossus. 

 Amtl. Ber. der 50 Vers, deutsche Naturf. u. Aertze in Miinchen, 1S77. 



Also: Zur Anatomic des Balanoglossus. Mittheil. aus der Zool. Stat. Neapel, 

 Bd. V, 1884. 



«1. c. 



«1. c. 



101. c. 



^^ Arthur Willey. Later Larval Development of Amphioxus, Quart. Journ. 

 Mic. Sci., Vol. xxxii, 1892. 



