188 J. B. Johnston 
greater than is shown in SCHAFFER’S figure, and that the sense cells 
are stained differently from the supporting cells. 
These organs arise in the embryo of Petromyzon in the epithelium 
covering the inner face of the branchial arch (DoHrn), in the same 
position in which they stand in the Ammocoetes. To this interesting 
fact is to be added another, namely, that although taste buds are 
present in the skin of the adult (20), they are apparently not present 
in the Ammocoetes stage. I have been unable to find them in several 
small and large Ammocoetes of Lampetra admirably fixed and stained 
for the purpose, and they are not present in the sections of P. dor- 
satus. 1 have not yet had suitable material to determine when they 
appear in the skin, but I can scarcely believe that I have overlooked 
them in the material which I have studied. It is not surprising 
that an animal which lives buried in the mud and takes for food 
whatever its respiratoy current brings to it, should not have taste 
organs in the outer skin. Those in the pharynx are in the position 
for the greatest effiecieney, and in fact in the only position where 
they would be of direct use. The important fact is that the organs 
are present in the entodermal lining of the pharynx in the Ammocoetes 
stage, and in the adult appear in the ectodermal covering of the body. 
The known facts regarding these organs seem to be: that they 
have the same histological structure and the same innervation as 
the taste organs in other vertebrates; that they arise in the ento- 
derm of the pharynx where they are found throughout larval and 
adult life; and that in the adult similar organs appear in the outer 
skin, where they would be of service during the free-swimming pe- 
riod. These facts suggest the following questions. Are these truly 
entodermal sense organs? If so, is not the lining of the pharynx 
the primitive location of the organs of taste? Are not the so-called 
multi-cellular glands of the tadpole pharynx also taste organs? 
Are such organs found in the pharynx of true fishes? Are the 
noticeable differences in form and size of the taste organs in the 
pharynx, the mouth and the outer skin due to modifications of the 
organs as {hey have spread more widely from their place of origin? 
The facts in Petromyzon give ground for the serious consideration 
of the hypothesis suggested by the writer (37) some years ago, name- 
ly, that the taste organs of vertebrates originated in the entoderm 
and secondarily spread to the outer surface of the head and body. 
I do not consider the very incomplete account which we possess of 
the taste buds in eyelostomes as eonelusive evidence in favor of this 
