192 , Balanoglossus. [ ZOE 
in the form of a pouch extending 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 tilla 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-ccelomic funnels in Amphioxus. These latter structures 
‘Alexander Agassiz. The History of Balanoglossus and Tornaria. Mem. 
Amer. Acad. Arts and Sci., Vol. ix, 1867. 
TJ. W. Spengel. Ueber den Bau und der Entwicklung des Balanoglossus. 
_ Amtl. Ber. der 50 Vers. deutsche Naturf, u. Aertze in Miinchen, 1877, 
Also: Zur Anatomie des Balanoglossus. Mittheil. aus der Zool. Stat. Neapel, 
Bd. v, 1884. 
se go 
‘ioc: 
sod 4 oe 
"Arthur Willey. Later Larval Development of Amphioxus, Quart. Vous 
Mic. Sci., Vol. xxxii, 1892. : 
’ 5 
