The Cranial Nerve Components of Petromyzon. 189 
hypothesis but only as suffieiently important to warrant further exami- 
nation with reference to this interpretation. 
Since writing the above the author has studied series of embryos 
of Oatostomus sp. and of Coregonus albus for a period of some days 
before and after hatching. In Coregonus the taste buds are less 
numerous than in Catostomus but otherwise the two species agree. 
(1) The taste buds are very much more numerous and are more 
highly developed in the pharynx than elsewhere. They are situated 
on the internal surface of each gill arch. (2) Behind the last gill 
taste buds are found in the oesophagus as far caudad as the opening 
of the duct of the air bladder. About sixty well developed organs 
were counted in the oesophagus of one speeimen of Catostomus. 
(3) Taste buds are found on the roof and floor of the mouth, where 
they are smaller than those in the pharynx and resemble those in 
the oesophagus. They are least numerous in the anterior part of 
the mouth. (4) No buds are found on the outer surface of the head 
or body except in the oldest specimen of Catostomus (some days 
after hatching) in which two buds were found on the upper lip just 
outside the mouth. In all the embryos examined the neuromasts of 
the head lines were well developed and the distinetion between 
neuromasts and taste buds was entirely elear. It seems from these 
facts that teleosts, in which taste buds are more numerous on the 
outer surface of the body than in any other class of vertebrates, 
agree with cyclostomes in the early history of these organs. The 
taste buds are numerous and well developed in the pharynx, oeso- 
phagus and mouth previous to the period of free life and appear 
in the outer skin when the young fish begins to swim about to seek 
its food. The great majority of the organs in the embryo, including 
the best developed ones, are situated in entodermal territory and all 
the facts thus far known favor the conclusion that taste organs in 
both eycelostomes and teleosts appeared first in the entoderm and 
later entered ectodermal territory. 'T'he mode of spreading from the 
pharynx to the surface of the head and body remains to be investi- 
gated. 
Somatie Motor System. 
The motor components require little comment. The eye-musele 
nerves have been discussed in the deseriptive part. It may be added 
that the assumption which has been made by anatomists that the 
small root arising with the trigeminus is a true abducens is an 
