Metazoa Obelia. 



229 



umbrella is made to pulsate and the gonophore to move. 

 The muscular fibres are cells which have become elongated 

 in one direction, and though still nucleated they show a 

 differentiation of the protoplasm which takes the shape of 

 a very marked transverse striation. In Hydra every cell 

 was sensitive to touch. 1 In the medusoid there are, scattered 



FIG. 119. MESODERMAL TISSUE FROM THE NECTO-CALVX OF 

 Aurelia aurita. (M. Schultze.) 



through the necto-calyx, special branched cells, which have 

 probably for their function the regulation of the muscular 

 movements, and, therefore, termed nerve-cells. These cells 

 and fibres are specially numerous near the edge of the bell. 

 Sensitive cells, since they convey to the animal the impres- 



1 There is some ground for believing that the processes of the ecto- 

 dermal cells of Hydra are nervous as well as muscular in function ; 

 hence the term ' neuromuscular ' applied to them. Jickeli has, more- 

 over, lately described true nerve-cells in Hydta. 



