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PLATE VIII. The co-operation between organiser and host tissues, (a) 

 Secondary embryo primordium, organised by one half of the blastopore lip 

 of an early gastrula. The graft (light pigmentation) produced the notochord, 

 flanked on either side by somite material, and the floor of the secondary 

 neural tube (s.n.). The host produced all the remainder, (b) Secondary 

 embryo primordium, organised by one half of the blastopore lip of a late 

 gastrula. The graft has formed only the notochord, and the somites of one 

 side. The host has produced all the rest. p.n. = primary neural tube; s.n. = 

 secondary neural tube; d. = lumen of the common gut. After Mayer. 



