smaller secretory cells, pear-shaped and lying between the bases of 

 the larger ones. These last mentioned cells are numerous in the 

 walls of the hypostome but fewer elsewhere. Their protoplasm is 

 granular and they stain deeper than the larger cells. 

 Make a drawing of each section. 



V. STUDY OF ISOLATED CELLS. 



Place living hydra on a slide, draw off the water and cover for a 

 few minutes with a drop of Mailer's Fluid. Cover and tap gently 

 upon the cover glass to separate the cells. 



Select and draw good examples of the varieties of cells mentioned 

 above. 



III. HYDRACTINIA OR PODOCORYNE SP. 



(Marine Hydrozoa). 



Examine with dissecting microscope a colony of Hydractinia on 

 a shell and note the way in which the shell is incrusted by the roots 

 or base ( hydro rhiza) of the colony, while the free portions, or stems 

 (hydrocaulis) arise from this base. 



With the compound microscope examine mounted preparations 

 of Hydractinia, and observe the following : isolated polyps or zooids 

 which have been torn free from the base. Among these are (i)Hy- 

 dranths or nutritive zooids with mouth opening surrounded by 

 circle of tentacles. (2) Blastosyles or reproductive zooids, without 

 mouth opening, with rudimentary tentacles, and with sex buds 

 (gonophores) in which ova and spermatozoa are found. (3) Dae- 

 tylozooids, or fighting polyps, without mouth or tentacles, but with 

 long slender body beset with nettle cells. 



Observe the cell layers characteristic of Coelenterates. 



Make drawings of all that yon have observed. 



IV. PENNARIA TIARELLA. (Marine Hydrozoa). 



Observe the form and manner of branching of the colony. Which 

 is the oldest polyp in the colony ? Which branch is the oldest ? How 

 many kinds of zooids do you find? 



In a stained and mounted specimen, observe the following : 



(1) The stem (hydrocaulis) containing a central gastro-vascu- 

 lar cavity ; surrounded by two layers of cells characteristic of 

 coelenterates ; the perisarc or cuticular covering, with rigid con- 

 struction. 



(2) The hydranth (nutritive zooid). How many circles of 



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