2 
MONICA TAYLOR. 
excited attention because, while possessing well-developed gill- 
lamellae on each of the four gill-arches, and typical Teleostean 
aortic arches, it yet spent a considerable part of the year 
buried in the mud like a Lepidosiren ( 5 ). Probably correlated 
with this habit of burrowing, and with modifications in the 
respiratory processes during the dry season, is the single 
median ventral branchial opening — a character which is 
described in the name Sym branch us. Other adaptations 
to this burrowing habit are probably the great length of the 
gill-chamber — the branchial opening being situated com- 
paratively far back — the vascular character of its lining, and 
also its almost complete separation from the exterior. Several 
members of this group possess accessory respiratory sacs, and 
J. Muller, in his work on the Myxinoids, says : Es wird 
wohl das obere Ende des Zungenbeins gemeint sein, denii 
liier sehe ich bei Symbranchus eine blinde Vertiefung jedoch 
ohne Sack, zwischen dem Zungenbein und dem obern Ende 
des ersten Kiemenbogens.^^ 
I have found the diverticulum referred to by Muller in the 
three adult specimens which I have examined — and indication 
of its future position in the older larvse. An account of its 
structure will be given in the section on the alimentary canal. 
The material for this work was obtained during an expedi- 
tion to the Gran Chaco in 1907, when Dr. Agar made the 
interesting discovery that the larva of Symbranchus has 
very well developed pectoral fins. Hitherto the absence of 
pectoral fins has been regarded as one of the characteristics 
of the group. The material consists of eggs and larvm 
preserved immediately after they were taken from the nest, 
and also of specimens reared under artificial conditions in 
tanks and dishes of water. In the latter case it was possible 
to record the rate of growth after hatching. 
Dr. Agar has given an account of his expedition in his paper 
on ^^Spermatogenesis of Lepidosiren paradoxa^^ ( 1 ), and 
to his field notes I am indebted for all the details relating 
to the nest of Symbranchus, the collection of the eggs, the 
habits of the living creature, while what I say regarding 
