SERTULARIA PUMILA Linnaeus 



Material. S. pumila is found growing on fucus and in 

 tide-pools along the Atlantic Coast. The student should receive a 

 colony with gonosomes (it is better to put the whole lot the night 

 before in glycerine), a stained colony, a cross-section through a 

 hydranth, and a longitudinal section through a gonosome. 



Descriptive Part 



Sertularia pumila is another common representative of the 

 class Hydrozoa. But unlike Pennaria it has no alternation of 

 generations, there being no medusa stage. It differs from 

 Pennaria also in that it belongs to the group of calyptoblastic 

 polyps in which the perisarc forms a protective covering or theca 

 for the hydranth and for the blastostyle. The method of bud- 

 ding is monopodial with terminal bud, 1 not with terminal or top 

 polyp as in Pennaria. The stem has as in Pennaria " unlimited" 

 growth, but the terminal bud never develops into a polyp. In- 

 stead, it produces at regular intervals two opposite buds which 

 remain sessile and become polyps. The result is similar to that in 

 sympodial budding inasmuch as the oldest polyps are nearest to 

 the hydrorhyza, but every pair of polyps has the same age, the 

 stem is not composite and the polyps take no part whatever in 

 its formation. The creeping hydrorhyza does not present any- 

 thing particular in its structure. The hydrocaulus or stem is 



1 The sympodial method is more common in calyptoblastic polyps and may 

 be best studied in Obelia. The polyps have limited growth. The polyp 

 nearest the hydrorhyza is the oldest, the end polyp the youngest. The main 

 stem is composite, the stem of every new polyp adding to its length. There 

 are gradations between the sympodial method and the monopodial method 

 with terminal bud. 



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