PHYSIOLOGY OF THE INVERTEBRATA. 31 1 



the nerve fibrils take a longitudinal course beneath the centre 

 of each series of paddles, and these are accompanied by 

 ganglionic cells, which become particularly abundant towards 

 the aboral end of each series. The eight bands meet in a 

 central tract at the aboral pole of the body ; but Eimer doubts 

 the nervous nature of the cellular mass, which lies beneath 

 the lithocyst, and supports the eye spots." 



Professor Huxley says that " the nervous system of the 

 Ctenophoran is, therefore, just such as would arise in Hydra^ 

 if the development of a thick mesoderm gave rise to the 

 separation and elongation of Kleinenberg's fibres ; and if 

 special bands of such fibres, developed in relation with the 

 chief organs of locomotion, united in a central tract directly 

 connected with the higher sensory organs. We have here, in 

 short, virtual, though incompletely differentiated brain and 

 nerves." 



In the Actinozoa, there is a plexus of fusiform ganglionic 

 cells connected by nerve-fibres at the base o£ the body ; and 

 at the base of the tentacula of the Actinia^ near the pigment- 

 cells (eyes ?) isolated nerve-cells have been discovered. 



The Echinodermata. 



Among these animals the nervous system consists of a 

 number of ganglia, connected by commissural cords, so as to 

 form a ring, from which nerve-fibres pass to various parts of 

 the body. 



" The internal nervous system of Ecliiniis consists of five 

 radial trunks, which may be traced from the ocular plates 

 along the anibulacral areas, external to the radial canals to 

 the oral floor, where they bifurcate and unite with each other, 

 so as to form a pentagonal nerve-ring. This ring lies between 

 the oesophagus and the tips of the teeth, which project from 

 the lantern. Small branches leave the ring and supply the 

 oesophagus, and lateral branches arise from the several trunks 

 to escape with the pedicels through the apertures of the pore 



