Landacre, Taste Buds of Amejiirus. 59 



20J mm. series there are more than 60 buds present in this 

 region. At their anterior limit they are continuous with the pos- 

 terior buds situated on the roof and the floor of the pharynx 

 and spread from this area backward. There can be little doubt 

 that we have here an actual spreading of buds, since the area oc- 

 cupied by buds in the 20J mm. embryo is more than four times as 

 long as that occupied in U, while the 20J mm. embryo is little more 

 than twice as long as U. The oesophagus is practically a straight 

 tube and the posterior buds are always less mature than those 

 farther forward. It should be noted here that the distribution 

 of buds being from anterior to posterior is also from the prox- 

 imal to the distal distribution of the nerves. It will be remem- 

 bered that this corresponds to the distribution of the buds on 

 the body. The prime fact seems to be the anterior-posterior 

 movement and the relation of buds to the proximal and distal 

 distribution of the nerves seems to be a secondary matter. 



16. SUMMARY OF PHARYNGEAL GROUP. 



The most striking characteristic of the pharyngeal group is 

 its complete segmental arrangement, an adaptation probably to 

 the more fundamental segmentation of the gill region. This 

 segmental arrangement is not confined solely to the gill, but is 

 present in the roof and floor buds as well. The spreading of 

 buds from anterior to posterior is almost as marked as in the 

 case of oral and cutaneous groups, if we except the distal hyoid 

 division. There is less evidence here that buds appear first on 

 the distal distribution of a nerve before they appear on the prox- 

 imal. In fact, the reverse occurs in the oesophageal buds and in 

 the case of the nerves supplying the distal hyoid groups. 



The oesophageal buds undoubtedly spread from the proxi- 

 mal toward the distal areas of distribution. It will be recalled, 

 in the case of the body buds, that the explanation seemed to be, 

 as indicated above, that the fundamental fact is the progression 

 from anterior to posterior; and in case of nerves innervating areas 

 morphologically posterior to their point of origin, the condition 

 would be reversed as compared with nerves innervating areas 

 anterior to their point of origin. We find no striking exceptions 

 to the method of progression, from anterior to posterior while 

 there are at least three well defined exceptions to the rule that 



