SERTULARIA PUMILA LINJNLEUS 25 



tentacles of Pennaria with nematocysts grouped in batteries. 

 The microscopic structure of the hydranth is generally speaking 

 the same as in Pennaria. 



Gonosome. The reproductive polyp or gonosome is much 

 larger than the trophosome. The gonotheca, usually called 

 gonangium has the shape of a ovoid sac with a truncated end and 

 is attached to the stem by a very thin and short pedicel or collar. 

 An opening is formed later when the so-called acrocyst pro- 

 trudes through the truncated end to the outside. The blasto- 

 style or modified polyp develops a gonophore w r hich appears as an 

 outgrowth of the ectoderm filled with reproductive cells. The 

 gonophore soon outgrows the blastostyle and almost fills the 

 gonangium. At the distal end of the gonophore a cuticle is 

 produced and the end of the gonophore protrudes now through 

 the gonangium. The cuticle of the gonophore expands forming a 

 globular sac or acrocyst into which the eggs pass. The remains 

 of the gonophore in the gonangium appear as irregular strands 

 called gubernacula. A new acrocyst is formed with the produc- 

 tion of a new gonophore. The male gonangia are more slender. 

 The egg develops into a planula which forms a new colony. 



Instructions 



1. Put a colony into a Syracuse dish with glycerine and exam- 

 ine it under the dissecting microscope. Make a half page draw- 

 ing showing hydrorhyza, hydrocaulus and branches with tropho- 

 somes and gonosomes. Number the polyps i-i, 2-2, 3-3 and 

 so on, beginning with the polyps nearest to the hydrorhyza, to 

 show the monopodial method of branching with terminal bud. 

 Number the branches a, b, c . . . and the polyps of one branch 

 ai_i, a 2 _2, a 3 -3 . . . and so on. 



2. Cut off a piece of the stem with expanded polyps and put it 

 on a slide in a drop of glycerine. Cover it with a cover glass and 

 examine under low power (50 diameters). Make a half page 

 drawing of two internodes showing the ccenosarc of the stem 



