ANTHOZOA HYDROIDA. 23 



Sertularia argentea, Plumularia falcata, &c. are subjected to 

 the same law, — the primary polypiferous shoots being deci- 

 duous, so that iu them also the stalk becomes bare, while the 

 upper parts are graced with a luxuriant ramification loaded 

 with tiny architects. But in our eagerness to generalize, 

 let us not forget that there are some species, as Sertularia 

 pumila, abietina, &c. in which this process of successive 

 denudation is not observable, — perhaps, however, because of 

 their form, which is not of a kind to be altered by it, and 

 hence unnoticeable, or because the duration of the whole is 

 too ftigitive to permit the law to produce a visible effect. 



There are facts which appear to prove that the life of the 

 individual polypes is even more transitory than their own 

 cells ; that like a blossom thev bud and blow and fall off or 

 are absorbed, when another sprouts up from the medullary 

 pulp to occupy the very cell of its predecessor, and in its turn 

 to give way and be replaced by another. When speaking of 

 flexible corallines Lamouroux says, " Some there are that are 

 entirely covered with polypi through the summer and autumn, 

 but they perish with the cold of winter : no sooner, however, 

 has the sun resumed his revivifying influence than new animals 

 are developed, and fresh branches are produced upon the old 

 ones." * Of the Tubularia indivisa, Sir John Gr. Dalyell tells 

 us that " the head is deciduous, falling in general soon after 

 recovery from the sea. It is regenerated at intervals of from 

 ten days to several weeks, but with the number of external 

 organs successively diminishing, though the stem is always 

 elongated. It seems to rise within this tubular stem from 

 below, and to be dependent on the presence of the internal 

 tenacious matter with which the tube is occupied. A head 

 springs from the remaining stem, cut over very near the root ; 

 and a redundance of heads may be obtained from artificial 

 sections, apparently beyond the ordinary provisions of nature. 

 Thus twenty-two heads were produced through the course of 

 550 days, from the sections of a single stem."-}* The ob- 

 servations of Mr. Harvey on the same, or a very nearly allied, 

 species of zoophyte confirm the experiments of Sir J. G. 

 Dalyell, so far as these have reference to the deciduousness of 



* CordU. Flex. p. xvi. 



+ Edin. New Phil. Joum. xvii. p. 415. 



