Landacre, Taste Buds of Ameiurus. 13 



still some variation may be due to this factor. Greater shrinkage 

 in an embryo in which a group of buds had appeared in an earlier 

 period would make the group seem to spread forward if measured 

 in sections from the anterior end. (2) All the earlier series 

 were not taken directly from the nest; for the first three days two 

 lots were taken each day and intermediate series were taken from 

 those brought in at a previous trip. Embryos reared in the lab- 

 oratory from the earlier stages until the time of hatching prob- 

 ably do not grow so fast and undoubtedly do not become so 

 thoroughly pigmented as those reared in the nest, but this prob- 

 ably does not materially affect the rate of differentiation of taste 

 buds in the series under discussion, since the mtervals were too 

 short. (3) The most puzzling question that arises in attempt- 

 ing to determine whether a group of taste buds, not located on 

 structures segmentally arranged, is actually spreading in a given 

 direction arises from the unequal growth of various regions of the 

 body. When we give the limits of a group of buds in various ages 

 in sections counted, as must be done sometimes, from the anterior 

 end of the body, we assume that the anterior end of the body is 

 a fixed point. This of course is not true. A group of buds might 

 show if measured m this manner a well defined spreading back- 

 ward and still not be spreading backward at all, but be simply 

 increasing in a given area which owing to the growth of that area 

 and of areas in front of it, comes to lie further from the anterior 

 end; or it might be moving bodily back with reference to other 

 structures near it. The branchial apparatus, for instance, owing 

 to its functional importance elongates much more rapidly than 

 other structures occupying similar segments of the embryo and 

 comes to occupy many more segments in the adult than in the 

 embryo (Johnston '05b), and the anterior taste buds situated on 

 the proximal hyoid and suspensorium move backward almost as 

 rapidly as the posterior buds, showing a backward movement 

 of these two structures, while on the other hand some portions 

 of the nasal group of buds remain practically stationary. 



For practical purposes in determining how fast and in what 

 direction a group is spreading the best means seems to be to reduce 

 the older embryo to terms of the younger in length. That is, if 

 a group of buds extended twice as far from the anterior end in 

 series B as in A and series B had increased less than twice as much 

 in length as A we would be warranted in thinking that the group 



