A HYDROID * (Pennaria). 



Examine a colony under the hand lens or low power of 

 the microscope, and notice the branching stem (hydro- 

 caulus), bearing on their tips the fleshy hydranths or 

 zooids. The hydrocanlus is covered with a horny, tube- 

 like perisarc. Does this present any striking peculiarities ? 

 Sketch the whole colony. 



In a single hydranth see that there is a balloon-shaped 

 body, the neck of the balloon being the proboscis, at the 

 end of which is the mouth. The hydranth is covered with 

 tentacles. Is there any regularity in their arrangement ? 

 Are they all similar ? Look on various hydranths for 



* For this purpose it is well to have some alcoholic material, and 

 also some mounted slides, which can be used, year after year, with 

 successive classes. To make these mounts the alcoholic material 

 should be washed for half an hour in water, and then stained for 

 twenty-four hours in alum cochineal (made by soaking 7 parts of 

 crushed cochineal insects and 7 parts of a'um in 700 of water for 

 twenty-four hours. Then boil until the amount is reduced to 400 

 parts. Allow to stand twenty-four hours, filter, and add a little 

 thymol to keep it from spoiling). After staining, the specimens 

 should be rinsed in water and placed in 80#, 95#, and absolute alcohol 

 for at least two hours each, and then left the same length of time in 

 oil of clove. The best specimens may then be selected, placed upon 

 the microscope-slides, the oil drained off, and a drop or two of Can- 

 ada balsam added, and a bit of thin glass (cover-glass) placed on the 

 specimen. The slides should be allowed to b come dry and hard 

 (which will take some weeks) before being placed in the hands of the 

 student. It must be borne in mind that all of the above details are 

 necessary ; omissions will result in failure 



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