NERVOUS SYSTEM OF THE TUNICATE 333 



SUMMARY OF THE RESULTS OF PREVIOUS INVESTIGATORS 



Since Hecht ('18) has carefully reviewed the literature of the 

 subject, I give below, from my own reading, only a brief summary 

 of the results of both neurohistological and physiological studies 

 made by earlier investigators. 



A. Neurohistological observations {Van Beneden andJulin, ^84) 



1. The ganglion consists of a central fibrillar substance 

 surrounded by a peripheral layer of cells. 



2. The largest cells lie to the outside. 



3. There are localized groups of cells chiefly at the anterior 

 end and on the ventral side of the ganglion which are suggestive 

 of motor centers. 



4. Large nerve trunks run forward to the oral and backward 

 to the aboral siphon. 



5. These break up into branches to form a nerve net about 

 the muscle fibers. 



6. There are said to be club, brush, and plate-like motor 

 nerve-endings present. 



7. No specialized sensory nerve-endings have been described. 



8. A cord of large ganglion cells extends down jnto the 

 viscera. 



9. The ganglion develops from the cerebral vesicle of the 

 larva. 



10. The visceral cord develops from the epithelial wall of the 

 central canal of the larval nervous system. 



11. The regenerating ganglion develops out of a derivative of 

 the same embryonic tissue from which the original ganglion 

 developed. (Schultze, '00). 



B. Physiological observations (for Ciona intestinalis) 



12. The siphons are the most sensitive parts. 



13. Rapid stimulation (prodding) is more effective than slow 

 continued pressure for the same intensity of stimulus (Poli- 

 manti, '10). 



