124 LABORATORY WORK. 



tentacles. Is there any regularity in their arrangement? 

 Are they all similar? Look on various hydranths for 

 globular outgrowths, medusa-buds. Sketch a hydranth 

 enlarged, showing the points made out. 



Study a mounted specimen under higher microscopic 

 powers, and see that the zooids are made up of two layers 

 and that they contain a central digestive cavity. Can you 

 trace the layers and the cavity into the hydrocaulus? 

 Could food taken into one of the hydranths pass to another 

 hydranth? Are the tentacles solid or hollow? Examine 

 the tip of a tentacle of the series nearest the mouth, and 

 see the large oval nettle-cells imbedded in it. (In favor- 

 able specimens threads can be seen extending from the net- 

 tle-cells.) Sketch a hydranth enlarged, showing layers, 

 digestive tract, etc., and a medusa-bud. 



Look carefully over the hydranths and see if you can find 

 any traces of an oesophagus turned into the body as in the 

 sea-anemone; of septa, and of mesenterial filaments. Do 

 any individuals show a bilateral nature? 



