PENNARIA TIARELLA. 21 



sponges. The presence of this layer- can not be demonstrated in this 

 exercise. 



The long tentacles are only slightly enlarged at the distal end, but the 

 short ones are very distinctly capitate. Note the numerous clear, 

 refractive bodies at the ends of both kinds of tentacles, and also down 

 one side of the long tentacles. These are the stinging capsules or 

 nematocysts, organs which serve for defense or for the capture of prey. 

 Each consists of a cell containing a poisonous fluid and a coiled hollow 

 thread which can be thrown out with some violence, numbing the 

 animals upon which Pennaria preys. 



Exercise 3. Draw a long tentacle, a short tentacle, and a portion of a stem 

 in the region where it branches. 



Exercise 4. Draw a hydranth having an attached medusa-bud; some of the 

 tentacles may be omitted. 



