176 THE ELEMENTARY NERVOUS SYSTEM 



is desirable. Such a form is to be found in Corymorpha 

 palma from the coast of southern California. 



Corymorpha palma is a beautifully transparent, sol- 

 itary hydroid of slender proportions (Fig. 43). Its 



stalk measures as much as 

 10 centimeters or more in 

 length with a diameter at 

 the thickest part of about 

 0.5 of a centimeter. Its 

 proximal end is anchored 

 in the mud and its distal 

 end carries a hydranth 

 that when expanded may 

 have a spread of 2.5 cen- 

 timeters. The proximal 

 portion of the stalk ends 

 in a blunt point and car- 

 ries rows of long filamen- 

 tous bodies, the frustules, 

 by which it is anchored in 

 the mud. This portion of 

 the stalk, often half a cen- 

 timeter or so in length, is 

 commonly turned nearly at 

 right angles to the rest, 

 which is held vertically 

 above the mud. A little 

 above the level at which the stalk emerges from the mud 

 it gains its maximum diameter; distal to this it becomes 

 gradually more and more slender till it reaches a narrow 

 neck, on which the hydranth is borne. The stalk itself is 

 marked by a series of longitudinal canals imbedded in its 

 more peripheral substance and running for the most part 



Fio. 43. Side view of the hydroid 

 Corymorpha, somewhat enlarged. 



