236 CHARLES R. STOCKARD 



Such reactions resemble in general the inhibiting effects of one 

 growing bud or organ over the growth of other buds in the plant 

 or organs in the embrj'o. 



The consideration up to this point has been limited to the 

 developing nervous system and its organs. Does a similar rela- 

 tion of linear and lateral growths and evidence of a similar com- 

 petition among organ buds exist in other systems of the embryo? 

 And, further, is there any evidence of a wider competition between 

 the different systems of the embryo? 



The development of the foregut from which is derived a large 

 portion of the alimentary tract in the vertebrate embryo is closely 

 similar in many ways to that outlined above for the nervous sys- 

 tem. The initial anteriorly directed conical evagination of the 

 entodemi first undergoes a linear development or growth, simply 

 becoming longer. When a certain length has been attained by 

 this early tubular foregut, here again lateral outgrowths begin to 

 appear, and a series of them is formed in order from the anterior 

 end backward in much the same way as the early neural tube 

 gives off the optic vesicles followed by the three primary brain 

 ventricles. The first and largest of the early foregut outgrowths 

 is the pair of mandibular pouches, in association with which the 

 mandibular arches arise to form the lower jaw. This pair of 

 outgrowths is soon followed by the hyoid pair and this by the 

 series of branchial pouches associated in later development 

 with the several gill arches. An outline scheme of these growths 

 is simply represented by the three accompanying diagrams in 

 figure 32. 



The further development of the alimentaiy canal also shows 

 in a very definite way a continuation of this process of lateral 

 outgrowths or buds to give rise to other organs. The lungs in 

 higher animals bud away from the floor of the entodermal canal 

 immediately behind the branchial pouches. And again in the 

 branchial region the thyroid and other glands arise by a definite 

 budding process from the epithelial wall. 



The development of the stomach itself is due to an excessive 

 proliferation or diffuse budding in a limited region, giving 

 finally the local sacculation in the otherwise narrow tube. Fol- 



