CHAPTER III 



THE CENTRAL NERVOUS SYSTEM OF ASCIDIANS 

 AND ITS SIGNIFICANCE IN THE MECHANISM 

 OF REFLEXES 



i. If we wished to observe the order of the natural 

 system in this book, we should not let the Ascidians 

 follow the Medusae. We consider it more profitable, 

 however, to discuss simple cases before taking up the 

 more complicated ones. Having reached the con- 

 clusion, at the end of the preceding chapter, that the 

 spontaneous coordinated activities in Medusae are not 

 due to specific morphological structures of the gan- 

 glion-cells, we will now attempt to find out whether 

 the reflex actions of animals depend upon the struct- 

 ure of the central nervous system or of the peripheral 

 parts. In Ascidians the central nervous system con- 

 sists of a single ganglion (d, Fig. 9). This ganglion 

 is situated between the oral and aboral tubes (a and 

 & Fig. 9). 



Ciona intestinalis (Fig. 9), a large, transparent 

 Ascidian, possesses a very characteristic reflex. If 

 either the oral or aboral opening be touched, both 

 openings close, and the whole animal contracts so 



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