338 M. C. Mereschkowsky on the Hydroida. 
completely smooth, in consequence of the form of the hydro- 
thecee, which more approaches that occurring in Thusaria, 
being entirely immersed in the chitinous substance, while the 
outwardly curved necks of P. mirabilis give a hispid aspect to 
its branches. 
Width of the branches of the middle of the colony 0°75 and 
0°85 millim., of the uppermost branches 1°10 millim. ; length 
of the hydrothece 0°52 millim. (at the end 0°57), their breadth 
0°34 millim. (at the end 0°45); length of the gonothece 0-9 
millim., their breadth 0°5. 
This species, which is a still more magnificent one than the 
preceding, is not more rare; but it is especially from the 
Glacial'‘Ocean (near the Swiatoy Nos) that I have collected 
the largest and most luxuriant specimens. 
Localities.—1. White Sea, near the promontory of Intzy 
(on the Zimnij bereg), in 66° N. lat. and 40° 25’ H. long., at 
a depth of 10 fathoms, on a stony bottom, June 23 (without 
gonophores) ; 2. Glacial Ocean, N.E. of the Swiatoy Nos, 
upon the Mourmansky bereg, in 68° 13!’ N. lat. and 40° KE. 
long., at a depth of 60 fathoms (the large specimens), upon 
a bottom of sand and shells, June 30, 1876 (with gono- 
phores). 
PROPOSITIONS. 
The following are the fifteen propositions, contained in the 
present memoir, which, I think, I can sustain and defend :— 
1. Forms like Syncoryne, Coryne, Gemmaria, Stawridium, 
Cladonema, Millepora, &c. form a type which I name the 
articulate type; all these forms are governed by the law of 
metamerism. 
2. Articulation is produced by incomplete transverse 
division. 
3. The very large number of metameres is produced by the 
law of physiological inertia of N. Wagner. 
4, The articulate form in the Hydroids is almost always 
accompanied by capitate tentacles ; tins form is the best adapted 
to fulfil the function of defence, the only function that remains 
to them when their position has become too distant from the 
mouth. 
5. The exceptions to this rule may be perfectly well ex- 
plained, and by no means contradict proposition 3. 
6. The hydranth with its tentacles may be regarded as a 
polymorphic colony (tentacles and body) composed of several 
Archhydre, Hiick., produced by the process of gemmation. 
‘he tentacles are not the homologues of such organs as feet, 
hands, &c. ; they are only their analogues. 
