26 NERVOUS SYSTEMS AND SENSE ORGANS 



nervous system was by Hertwig, 1880. A subepithelial nerve plexus 

 with the bipolar and multipolar cells has been described and figured. 

 Bethe, '95, also describes and figures a network of nerve cells and 

 fibers in ctenophores. 



The characteristic aboral sense organ was first described by 

 Edwards, 1841. At a later time Chun, 1878, describes and figures 

 it in detail showing the little otocyst with its group of calcium 

 crystals supported on four bands of fused cilia like a little table, 

 with each tip of the leg coming into relation with two of the eight 

 ciliary bands. 



This peculiar balancing organ has been considered in a way to 

 represent a central nervous system because of its reaction to the 

 ciliary bands. These bands seem not to be under the control of the 

 nerve cells and fibers, but some are of this opinion. The nervous 

 system then would not relate to the cilia, but in some way there 

 is a coordination of movement in the eight ciliary bands. That this 

 is not as simple as might at first seem is shown by the fact that the 

 efli'ective stroke is in the opposite direction from the wave of ciliary 

 action, so that the simple explanation of the movement of one cilium 

 aflfecting the next, like a row of tenpins, does not hold. 



Bauer, 1910, found by gently touching the mouth region of a 

 ctenophore, that it stopped its cilia. If vigorously stimulated 

 its plates vibrate more actively for a short time. If the aboral 

 sense organ be removed the same reactions apply as before. He 

 concludes from this that the reactions cannot be ascribed to the 

 sense body but must depend upon the action of the diffuse nervous 

 system which although chiefly concerned with the muscles of the 

 cetenophore seems also to have an influence on the rows of swim- 

 ming plates. 



Gothlin in a recent paper, 1920, on the study of ciliary move- 

 ments finds that the primary inhibition of the ciliary movement 

 is probably due to cilio-inhibitory nerves. Receptors at the surface 

 of the body transfer their impulses to the nerve-net. These in turn 

 transmit them to the end apparatuses which inhibit the vibrations 

 of the swimming plates, probably blocking the neuroid conduction 

 between them. There is an intimate connection between primary 

 and secondary inhibitory mechanisms. Both probably use the same 

 receptors, but the primary mechanism functions on impulses of 

 weaker intensity. 



Abbott, 1904, who has studied the interesting worm-like Coelo- 

 plana has found a rudimentary nervous system with four ganglia 

 symmetrically disposed about the otolithic capsule. Just outside 

 the otolithic capsule in the angles formed by the intersecting tenta- 

 cular and .sagittal planes are four large nerve ganglia that send off 

 fibers to form a sort of diffuse peripheral system and supply fibers 

 that cover part of the capsule as an enveloping sheath. Each gang- 



