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PRINCIPLES OF EMBRYOLOGY 



be guaranteed to detect the most minute traces of antigens, and it is 

 possible that substances which seem suddenly to appear during develop- 

 ment may have been present in undetectable amounts at earlier stages. 



Bearing this caution in mind, Clayton's results were as follows. She 

 was able to detect six different antigenic substances (proteins?) in the 

 blastula to neurula stages. She divided these into (i) a C or common 

 group, which occur in both the ectoderm and mesoderm of the gastrula. 

 Part of this fraction (C) is already present in the blastula, but another 

 part (C^) arises after or during gastrulation, and is presumably synthesised 

 at that time. There are also (2) an E or ectoderm group and (3) an M or 

 mesoderm group, which are confined to the ectoderm or the mesoderm 

 respectively. Again in both these groups there are some components 

 (E and M) which occur in the blastula, and others (E^ and M^) which 

 arise during gastrulation. In the blastula, the E and M antigens are thought 

 to exist side by side, only becoming segregated into different tissues as 

 gastrulation proceeds. Similarly, the CC^ EE^ antigens of the gastrula 

 ectoderm become sorted out between the neural plate and the ectoderm 

 of the neurula. The former probably receives mainly CE^ and the latter 

 C^E, but the identifications cannot yet be made with certainty. New anti- 

 gens also appear during neurulation, e.g. a fraction named Y (Fig. 10.16). 



Figure 10.16 



Diagram of the antigenic fractions found in various regions of the newt 

 embryo. (From Clayton 1953.) 



