38 Cincinnati Society of Natural History. 
artery is found in certain Caducibranchiata. In these cases, a 
“rete mirabile ”’ persists in the course of the ductus, and rep- 
resents the obliterated gill. (Balfour, Comp. Embryol. Vol IT.) 
Since the ‘‘ductus Botalli” is a constant feature in all 
specimens of Adellostoma examined, its significance lies in 
D, efferent branchial system of Bdellostoma forster?, dorsal view. 
K, heart and afferent branchial system, of Bde//ostoma forstert, ventral view. 
Ap. posterior dorsal aorta. 
Aa, anterior dorsal aorta. 
Car, right carotid. 
Cal, left carotid. 
ef. br, efferent branchial artery. 
rv, ring vessel of gill passage. 
S, sinus venosus. 
A, auricle. 
V, ventricle. 
Av, ventral aorta. 
afb, afferent branchial artery. 
z, body on ‘‘ductus Botalli.” 
g, gill pouch. 
gpe, external gill passage, 
oed, oesophago-cutaneous duct. 
the fact that even in the 13-gilled forms, we have to do with 
a reduction rather than an zucrease in the primitive number of 
gills. The embryological development, according to Price 
(Some Points in the Development of a Myxinoid. Verhl. der 
Anat. Ges., 1896), renders this conclusion certain. A large 
26 
