192 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
Amia. The arrangement and innervation of the lateral line sense 
organs (canal organs and pit organs) in Amia and Lepidosteus 
are almost identical, allowing for the much elongated body of the 
latter. The gular series of pit organs in Amia is, however, lack- 
ing in Lepidosteus. The most striking difference between the 
cranial nerves of the two species is the total lack of a ramus 
mandibularis internus in the facial nerve of Lepidosteus. 
In Polyodon we see an enormous development of lateral line 
sense organs, chiefly on the exaggerated rostrum and the elong- 
ated gill-cover. The so-called “primitive-pores” of Polyodon are 
certainly sense organs, and supplied by lateral line fibers of the 
seventh, ninth and tenth nerves, chiefly from the seventh, possibly 
exclusively so. Whether the primitive pores correspond to pit 
organs or to the ampullae of Lorenzini of the elasmobranchs the 
writer does not as yet have any decided opinion. The medulla 
oblongata of Polyodon possesses a large lateral line lobe into 
which enters the greater part of the lateral line elements of the 
seventh nerve. This lobe is an elasmobranch character and is 
lacking in Amia and Lepidosteus. Another elasmobranch charac- 
ter in Polyodon is the sharp distinction between the branches of 
the trigeminal and facial nerves. There is never any anastomos- 
ing between these nerves, such as is seen in Amia and Lepidosteus. 
Taste-buds are few and found externally' only in the region of 
the mouth (Allis). The anterior extension of the ramus pala- 
tinus facialis is small, almost rudimentary. The rudimentary 
barbels are supplied by vestigial twigs from the ramus palatinus 
VII and the ramus maxillaris V, but no sense organs of any kind 
have been found on the barbels. 
It would seem that there should never have been any doubt 
that the “primitive pores” of Polyodon are strictly comparable 
to the “nerve sacs” of the sturgeons. They are similar structures, 
parts of the lateral line system. In the true sturgeons, however, 
the lateral line organs are not so extensively developed as in 
Polyodon, and the nerve sacs are more aggregated than the primi- 
tive pores. In Scaphirhynchus (and in Acipenser, presumably) 
there is a great development of tasite-buds. These, however, are 
not generally distributed in the skin, as in Amia and Lepidosteus, 
but occur in great abundance on the two pairs of barbels and the 
oral fringes. In consequence the trigeminal and facial nerves are 
as sharply distinct as in Polyodon, only certain peripheral parts 
of the ramus palatinus VII and the ramus maxillaris V uniting 
to supply the barbels. 
