62 PATTERNS AND PROBLEMS OF DEVELOPMENT 



usual shaking.'* Neither of these two methods provides for the rather re- 

 mote possibihty of production of other gaseous or volatile acid-forming 

 substances or for production of ammonia. 



As regards the problem of developmental pattern, it is much more im- 

 portant to know whether a respiratory pattern is present in eggs and early 

 developmental stages, and what changes it may undergo during develop- 

 ment, than to determine whether such pattern is present in adult indi- 

 viduals; but the difficulties are even greater. Although the data thus far 

 obtained with adult forms give no information concerning earlier stages, 

 they are of some interest to developmental physiology because, in those 

 cases in which evidence of a respiratory gradient has been obtained, this 

 gradient parallels gradients indicated by other methods, and in some forms 

 these other gradient expressions persist from early development through- 

 out life, at least in certain parts of the body. Gradient patterns indicated 

 by differential susceptibility, differential dye reduction, and in other ways 

 are characteristic of early developmental stages; and their coincidence 

 with respiratory gradients in fully developed individuals suggests the 

 possibility that a respiratory gradient pattern may also be present in 

 earlier stages of development. Granting the possibility of sufficiently ac- 

 curate determination, however, separation of the unfertilized or fertilized 

 egg into pieces leaves the nucleus in one piece if it is not destroyed or in- 

 jured, although in many eggs fertihzation of the nonnucleated piece is 

 possible. Separation of blastomeres and of parts of embryos and larval 

 stages is possible, but the same questions as to effects of separation arise 

 as with pieces of adult animals, and the possibihty of periodic change in 

 respiratory rate in connection with the cell-division cycle must also be 

 considered. As development progresses, localization of organs and appear- 

 ance of new axes may introduce further complication. Respiration of parts 

 of amphibian embryos isolated by section has been determined by J. 

 Brachet (1934a, b, c, 1936), and more recently determinations have been 

 made on different regions of intact unfertilized eggs and embryos by intro- 

 duction of a single egg or embryo into a capillary tube with diameter of 

 lumen equal to, or slightly smaller than, that of the egg and connection 

 of both ends of the tube with a microrespirometer (J. Brachet and Sha- 

 piro, 1937). With this method the organism is not injured in any way, and 

 oxygen uptake of two opposed sides can be determined separately. Re- 

 sults obtained in this way are discussed in the following chapter. Still 



■• See Appendix I, p. 731. 



