SERTULARIA. 187 



boundary, separating it from the lower or under part of the branch. — 

 Figs. 1, 2. 



Above 30 boughs originate from the most luxuriant specimens. 



The hydra inhabiting the denticle is retractile completely within, 

 whence it rises to protrude a long neck, with from 25 to 27 muricate ten- 

 tacula. It appears somewhat gross, the tentacula stout, and often much 

 recurved or curled, previous to their full extension. — Figs. 3, 4, 9. 



The whole product is greenish, of more vivid colour when young ; the 

 stem dark umber if old ; and the hydra pale green. 



Specimens are founded on old shells. When torn off, a small tuft 

 separates along with the root. 



Probably the stem and subordinate parts are invested by skin, which 

 is perfectly transparent, and wherein the contraction denoting articulations 

 is perceptible. However, the structure of the stem itself, farther than con- 

 sisting of tubuli, and in being porous like wood, is not quite obvious. 

 These features are seen below in the thicker parts ; but above, the parts 

 resolve into a single tube. 



Regeneration. — While investigating the structure, I cut over some 

 specimens near the root in December, and subdivided the sundered stalk of 

 each into several portions. Vigorous reproduction followed. In five days, 

 seven shoots, about the fifth of a line, or the sixtieth part of an inch long, 

 were descending from the lower extremity of one of the sections ; and next 

 day, the prolongation of all still continued advancing in the same direction, 

 downwards, inverse to that of nature, which is upwards. — Fig. 5. 



Shoots more numerous and more vigorous descended also from other 

 sections. Nine descended from one of them. 



Another section, an intermediate portion of a stalk, an inch long, 

 generated several shoots from both extremities. The vegetation advanced 

 luxuriantly — more so from the lower than from the upper extremity. Two 

 hydrse were developed here, and one fi'om a shoot of the upper extremity 

 in 27 days. This section had been kept in a horizontal position. 



Shoots in an early stage are white. The specimens now under expe- 

 riment had been procured on December 14. A section only four lines in 

 length was made on the 16th. Vegetation issued from both extremities. 



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