390 EVENINGS AT. THE MICEOSCOPE. 



sisting between the polypary and its associated organs, 

 all combine to form an object of the highest in- 

 terest, and indicate that, in this fixed yet travelling 

 zoophyte, we have a type of structure transitional 

 between the dendritic HydroidcB and the more highly 

 organized Acal&ph. In the simplest acalephoid form, 

 such as the medusoid of CoiwpanuLaria [or Laomedea^ 

 (which is nothing more than an extension of the poly- 

 pary specially organized for independent and motile 

 life,) we have (as in Hydractinid) an expanded poly- 

 pary, represented by the umbrella, and permeated 

 by vascular tubes from the confluence of which last 

 spring, at the centre, the tentaciilar polyps, various in 

 number; and between them the reproductive polyps, 

 represented by the sessile generative sacs." * 



You see here a jai', on the glass side of which 

 are traced a number of very fine white lines, barely 

 discernible by the unassisted eye. But by the aid of 

 the lens you see that each line is a long and slender 

 thread, which creeps along the glass, and at length 

 starts out from it free for a short distance, and is then 

 terminated by a long club-shaped body, which carries 

 at its extremity four horizontally divergent organs, like 

 the arms of a turnstile. Tracing down the threads to 

 their lower extremities, you see that they are branches 

 of one thread, which creeps irregularly over a filamen- 

 tous sea- weed growing from a stone in the jar. The 

 sea-weed had been in the vessel for several weeks, and 

 the water having been undisturbed, the knobbed 

 thread, which was originally confined to the plant, 

 continued to grow, and coming into contact with the 

 glass spread upon it. Many other threads have ex- 

 * Ibid., op. cit. 



