392 REPORT—1863. 
polypite with its clusters of gonophores, having finally attained complete 
maturity, is then in its turn cast off, to be succeeded in an entirely similar 
way by a new one. 
The formation of successive polypites is always accompanied by a periodical 
elongation of the stem, and this is indicated by annular markings of the 
periderm separated by rather wide intervals, each interval corresponding to a 
single decapitation and renewal. 
From the above description it will be seen that the formation of successive 
polypites is not so much a process of ordinary budding, as a true metamor- 
phosis of the decapitated extremity of the coenosarc. 
In connexion with the phenomena now described, those which accompany 
the artificial section of the stem may here be mentioned. When the stem is 
cut across, the ccenosare of the upper segment soon heals over at the place of 
section, the tubular lacunz become again closed, and the ccenosare now begins 
to grow downwards through the cut extremity of the periderm, presenting 
the same lacunar structure as in the older portions, and excreting upon its 
surface a very delicate periderm. The well-known cyclotic currents may 
generally be seen with great distinctness in the fluid which fills the tubular 
lacune of the young elongated coenosare. 
The lower segment, on the other hand, instead of pushing forth from the 
cut extremity a simple continuation of the ccenosarc, developes from this ex- 
tremity a polypite*. ‘There is thus manifested in the formative force of the 
Tubularia-stem a well-marked polarity, which is rendered very apparent if a 
segment be cut out from the centre of the stem. In this case, no matter in 
what position the segment may lie, that end of it which was directed down- 
wards or proximally while it formed a part of the unmutilated hydroid will 
never develope a polypite, but will extend itself as a simple cylindrical pro- 
longation of the ccenosare ; while the upper or distal end, instead of becoming 
simply elongated, will shape itself into a true polypite ; and all this though of 
course not the least difference in structure or form can be detected between 
the two extremities at the time of section. 
It is further manifest from these facts that when the hydroid is placed under 
conditions which allow of perfect freedom of growth, there is no such thing 
as a stationary extremity, both ends being really growing ends, while there 
exists in every segment a neutral plane midway between the two ends. 
Polypite-bud in the Campanularida and Sertularida.—In the development 
of the bud, the Campanularian and Sertularian hydroids differ in some im- 
portant features from those which characterize the process just described. It 
may be easily watched in many species, as, for example, in Laomedea flexuosa. 
We may here see it proceed, in the first place, to the formation of a hollow 
cylindrical branch, whose cavity is in free communication with that of the 
coenosarc, and whose distal extremity ends in a cul-de-sac invested, like 
the rest of the young branch, by the chitinous periderm. Up to this point 
the phenomena are precisely similar to what we have just seen in the Tubu- 
larida; but now the distal extremity of the branch begins to enlarge, and at 
the same time continues to coat itself with a chitinous periderm in the form 
of a capsule, which acquires increased thickness by successive deposits of 
new matter to its inner surface, thus contrasting with the thin pellicle which 
forms the temporary capsule in certain Tubularida. 
' The extremity of the branch now presents the shape of an inverted cone, 
* The observations of Dalyell, who has made numerous experiments on the section of 
the stem in Tubularia indivisa, are here quite in accordance with my own. (See Dalyell, 
‘Rare and Remarkable Animals,’ vol. i. p. 23.) 
