A HYDROID (Pennaria). 



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 or 

 for an hour in borax carmine. 



After staining, the specimens should be 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 Canada balsam added, and 

 a bit of thin glass (cover-glass) placed on the specimen. The 

 slides should be allowed to become 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. 



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 hydrocaulus is covered with a horny, tube- 

 like perisarc. Does this present any striking peculiarities? 

 Sketch the whole colony, making the hydranths half an 

 inch in length. 



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 



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