70 INVERTEBRATE ZOOLOGY. 



and conditions — expanded, contracted, buds, empty cups, etc. Branches, the 

 members of which lie approximately in one plane, are the best for this pur- 

 pose. 



33. Mark out on a sheet of white paper a series of rings the size of 

 watch crystals, and designate as follows : 



Place watch crystals on these and fill with the corresponding liqiiids. Use 

 a solid watch-glass for the 100^ and keep it covered. Drop the branches se- 

 lected into the borax carmine and let them stay 5-10 minutes, iintil deeply 

 stained. Then transfer successively to the different watch crj-stals, 4-5 min- 

 utes in each. Use a needle for this, but do not break or prick the specimens. 

 From the turpentine spread out the branch on a slide in a small drop of bal- 

 sam. Cover and examine. The living protoplasmic portion is colored pink 

 and consists of the polyps and irregular connecting stems between them, run- 

 ning through the centre of the branches. The whole is invested by a trans- 

 parent chitinous skeleton, the peris-arc, which encloses the stems and expands 

 into a cuji about each polyp. Study details as follows : — 



a) A feeding polyp or Hydranth. The body is divided by a constriction 

 into a terminal portion (manubrium) which bears the tentacles, and an ex- 

 panded basal portion. How many tentacles are there ? Is the number con- 

 stant ? What can be seen upon these with the high jiower ? The basal por- 

 tion is hollow, containing the gastrocoele, or gastro-vascular cavity. Around 

 the hj'dranth is an exi)anded ciip, the hydrotheca. Can a polj'p entirely re- 

 tract into this ? In this species the hydrotheca has the shape of a bell {cavi- 

 panula), hence the name. Just below the polyp the perisarc is divided into 

 rings or joints. What is the probable use of them? Is their number con- 

 stant ? Does it bear any relation to the age or size of the polp V 



b) A reproductive polyp or Blasiostyle. This is merely the stalk which 

 bears round medusa-buds ; it may be considered a reduced polyp, elongated in 

 shape, and without mouth or tentacles. It is siirrounded by a cup, the 

 Gonotheca. Compare with a hydrotheca. 



c) Mediisa-buds. These are produced as V)uds from the sides of the Blasto- 

 style. Which of these are the most mature? In what direction does growth 



