THE ASCIDIANS AND AMPHIOXUS II7 



the result of a process of induction, and we can see the first signs of this 

 in the ascidians. But in the ascidians the primary inductions occur during 

 the early cleavage divisions, v^hile in the higher vertebrates they happen 

 much later. 



SUGGESTED READING 



The papers of Conklin 1905, 1932, are classics of descriptive embryology. In addition 

 Rose 1939, Reverberi 1948, Dalcq 1938, pp. 103-27. 



no brain or palps, and the vegetative anteriors endoderm and notochord but 

 no neural tube. 



{b) If the anterior vegetative cells are removed, the rest does not develop the 

 brain and palps (although the anterior animal cells from which they should 

 form are still present), nor neural tube. 



(c) If the anterior animal cells are removed, and the brain and palps are again 

 absent. 



{d) The anterior animal couple are removed and replaced by a posterior 

 animal couple (shaded). StiU the brain and palps are absent. 

 (After Reverberi 1948.) 



