710 
The ventral surface of the small end is soon fastened to some solid 
substance, and the invaginated portion is protruded and pours out its 
cement. Even in specimens with two or three fully formed hydranths 
the gland which is thus formed may be seen, as a flat part of ectoderm 
cells, at the proximal end of the hydrorhiza. After fastening itself the 
planula elongates, and forms a layer of perisarc, by means of which it 
is fastened throughout its whole length. It does not become a hydranth 
but a hydrorhiza, and the first hydranth is formed as a bud, which 
grows out at right angles to the long axis at the end opposite the 
adhering gland. As soon as the first hydranth has acquired tentacles 
and a mouth, a second bud grows out close to the base of the first, aud 
so on; the portion which is formed from the body of the planula per- 
sisting as a root without buds. 
The formation of the first hydranth from the planula is therefore, 
in this species at least, a process of metagenesis rather than a meta- 
morphosis, and this is also the case in Hydractinia, where the planula 
becomes a root, and produces the first hydranth by budding. 
The planula of Turritopsis has an invagination at its small end, 
and more careful study will undoubtedly show its presence in other 
species. 
The young hydranth of Eutima has a tentacular web, and the ten- 
tacles are situated in definite radii. ‘There are five equidistant large 
tentacles, which are the first to appear, and alternating with these, five 
smaller and younger secondary or interradial tentacles. 
The distribution of the tentacles of hydroids with reference to de- 
finite radii, does not seem to be at all unusual. Hamann who calls 
attention to the fact in Podocoryne Heckelu (Jen. Zeit. XV. 1882) 
says that this is the only instance known, although he suggests that 
further research may show that it is not unusual. 
The tentaculated planulae of Aegineta and Aeginopsis figured by 
Metschnikoff (Z. Z. XXIV) must, as I believe, be regarded as 
hydrae, and in these the four primary tentacles are definitely arranged, 
just as they are in Podocoryne Heæckeli. 
In the American Cunina ‘octonaria (McCr.) the larva is a true 
hydra, with mouth and stomach, and with no traces of an umbrella or 
of some organs. It gives rise to other hydras by budding, and in the 
egg-embryo, as well as in the buds, there are at first two opposite 
tentacles; two more soon appear at right angles to the first, as in Aege- 
nata, and much later four smaller ones are developed in alternation 
with the four primary ones. 
I believe that the young Liriope is essentially a hydra, with ac- 
