SCIENTIFIC SUMMAKY. 
435 
magnetic than the palladium in a free state. As a matter of fact, however, 
this was found not to be the case. In short, the palladium charged with 
hydrogen was, according to Graham, more magnetic than in its ordinary 
state. Palladium is but feebly attracted by a magnet, but the hydrogenized 
palladium is much more powerfully attracted. The cause of the anomaly 
has been a fruitful source of dispute, and has led M. Blondlot to set to work 
and repeat Graham’s experiments afresh, in order to see whether the dis- 
crepancy really exists. His results are in all cases diametrically opposed to 
those of Graham. In fact, he finds that the palladium, when charged with 
hydrogen, is much less attracted than when in a free state ; thus showing 
that hydrogenium, like gaseous hydrogen, is diamagnetic. It is believed 
that Graham’s curious results were due to impurities in the materials with 
which he experimented. — Comptes rendus , lxxxv. p. 68, July, 1877. 
ZOOLOGY. 
A One-armed Hydroid. — Under the name of Monobrachium parasitum , M. 
Mereschkowsky describes (“ Ann. and Mag. Nat. Hist.,” September, 1877), 
a most remarkable form of hydroid polyp discovered by him in the White 
Sea, where it lives at depths not exceeding five fathoms, adhering to the front 
end of the shell of the common Tellina solidula. The hydrorhiza in this 
singular polyp is represented by a sort of membranous expansion, from 
which the hydranths rise, and are surrounded for about one-fourth or one- 
fifth of their height by a chitinous tube, which the author regards as repre- 
senting the hydrocaulus. The hydranth itself is a little, nearly cylindrical 
yellowish body, about one-twelfth of an inch long, truncated above, where 
it terminates in a simple rounded aperture. The single tentacle, which is 
filiform and very long, springs from one side of this primitive polyp-body a 
little above the middle. The gonophores or reproductive bodies are scat- 
tered among the ordinary hydranths, and spring, like them, from the mem- 
branous expansion. They have a short, thin stem, above which they are of 
an oval form, truncated above, and each of them develops in its interior a 
medusiform planoblast, having four radiating canals, each with two genera- 
tive sacs, and sixteen tentacles. M. Mereschkowsky regards this hydroid as 
constituting the type of a distinct family of Athecata (Monobrachiidse), nearly 
allied to the almost equally singular Lar sabellarum of Gosse, which possesses 
two tentacles. He points out that both these species, which are so scantily 
supplied with tentacles, take up their abode in peculiar positions Lar 
upon the very margins of the tubes of Sabellce , and Monobrachium upon one 
end of the shells of Tellince, in both cases in the spot where, by the exertions 
of the host, an abundant supply of nutriment will be brought easily within 
their reach. The great development of the tentacle in Monobrachium (it is 
three or four times as long as the body) he explains by the greater amount 
of nourishment which can be applied to the support of this single organ, 
coupled with the greater activity which it is obliged to display when com- 
pared with the tentacles of other hydroids. From a consideration of the 
characters of this and other hydroids, M. Mereschkowsky comes to the con- 
clusion that the fundamental number in the hydroids is not four, as generally- 
