SCIENCE. 
45 
some distance above it, while in Limnocodiutn the ridges 
are direct continuations of the tentacles whose structure 
they retain. They become narrower as they approach the 
margin. 
The number of the tentacles is very large in aduit speci- 
mens. The four tentacles which correspond to the direc- 
tions of the four radial canals, or the perradial tentacles, are 
the longest and thickest. The quadrant which intervenes 
between every two of these carries, at nearly the same 
height above the margin, about thirteen shorter and thinner 
tentacles, while between every two of these three to five 
much smaller tentacles are given off from points nearer to 
the margin, and at two or three levels, but without any 
absolute regularity ; indeed, in the older examples all regu- 
larity, except in the primary or perradial tentacles, seems 
lost, and the law of their sequence ceases to be apparent. 
I could find no indication of a cavity in the tentacles ; but 
they do not present the peculiar cylindrical chord-like 
endodermal axis lormed by a series of large, clear, thick- 
walled cells which is so characteristic of the solid tentacles 
in the Trachomedusae and Narcomedusas. From the solid 
tentacles of these orders they differ also in their great ex- 
tensibility, the four perradial tentacles admitting of exten- 
sion in the form of long, greatly-attenuated filaments to 
many times the height of the vertical axis of the umbrella, 
even when this height is at its maximum ; and being again 
capable of assuming by contraction the form of short thick 
clubs. Indeed, instead of presenting the comparatively 
rigid and imperfectly contractile character which prevails 
among the Trachomedusae and the Narcomedusae, they 
possess as great a power of extension and contraction as 
may be found in the tentacles of many Leptomedusae (Thau- 
mantidae, &c.) These four perradiate tentacles contract in- 
dependently of the others, and seem to form a different 
system. All the tentacles are armed along their length with 
minute thread cells, which are set in close, somewhat spir- 
ally arranged warts. 
The lithocysts or marginal vesicles are, in adult speci- 
mens, about 128 in number. They are situated near the 
umbrellar margin of the velum, between the bases of the 
tentacles, and are grouped somewhat irregularly, so that 
their number has no close relation with that of the tentacles. 
They consist of a highly refringent spherical body, on which 
may be usually seen one or more small nucleus-like cor- 
puscles, the whole surrounded by a delicate transparent 
and structureless capsule. This capsule is very remarkable, 
for instead of presenting the usual spherical form, it is of 
enlongated piriform shape. In its larger end is lodged the 
spherical refringent body, and it thence becomes attenuated, 
forming a long tubular tail- like extension which is continued 
into the velum, in which it runs transversely towards its 
free margin, and there, after usually becoming more or less 
convoluted, terminates in a blind extremity. 
The marginal nerve-ring can be traced running round 
the whole margin of the umbrella, and in close relation 
with the otolitic cells. Ocelli are not present. 
The generative sacs are borne on the radiating canals, 
into which they open at a short distance beyond the exit 
of these from the base of the manubrium. They are of an 
oval form, and from their point of attachment to the radial 
canal hang down free into the cavity of the umbrella. 
Some of the specimens examined contained nearly mature 
ova, which, under compression, were forced from the sac 
through the radial canal into the cavity of the stomach. 
While some of the characters described above point to 
an affinity with both the Trachomedusae and Narcomedusae, 
this affinity ceases to show itself in the very important 
morphological element afforded by the marginal bodies. 
In both Trachomedusae and Narcomedusae the marginal 
bodies belong to the tentacular system ; they are metamor- 
phosed tentacles, and their otolite cells are endodermal, 
while in the Leptomedusae, the only other order of craspe- 
dotal Medusae in which marginal vesicles occur, these 
bodies are genetically derived from the velum. Now in 
Limnocodium the marginal vesicles seem to be as truly 
velar as in the Leptomedusae. They occur on the lower 
or abumbral side of the velum, close to its insertion into 
the umbrella, and the tubular extension of their capsule 
runs along this side to the free margin of the velum, while 
the delicate epithelium of the abumbral side passes over 
them as in the Leptomedusae. It is true that this point 
cannot be regarded as settled until an opportunity of trac- 
ing the development is afforded ; but in very young speci- 
mens which I examined I found nothing opposed to the 
view that the marginal vesicles were derived, like those of 
the Leptomedusae, from the velum. 
Important points still remain to be cleared up regarding 
the development of Limnocodium and the determination of 
the question whether the Medusa be derived from the egg 
directly or only through the intervention of a hydranlid 
trophosome. I have arranged, with Mr. Sowerby, some 
methods of observation by which I hope to obtain data for 
determination of these points. 
If this be the case Limnocodium will hold a position in- 
termediate between the Leptomedusae and the Trachome- 
dusae ; but as the greatest systematic importance must be 
attached to the structure and origin of the marginal vesicles, 
its affinity with the Leptomedusae must be regarded as the 
closer of the two. Geo. J. Allman. 
THE ELECTRIC LAMPS OF M. TCH 1 KOLEFF. 
M. Tchikoleff, the head of the electric lighting depart- 
ment of the Russian artillery, has addressed to La Lumiere 
Electrique a communication, of which the following is a 
translation, in which he claims that the application of de- 
rived currents which has been successfully adopted with 
the lamps of MM. Lontin and Siemens, was employed by 
him as far back as the year 1871. 
“ Having experimented for a lengthened period with the 
Foucault and Serrin regulator lamps, which were con- 
sidered to be the best at the period when I took up the 
question, I was able to observe in them the following 
defects : 
1. Several lamps, arranged in series or in multiple arc in 
a circuit, would not continue to work. 
2. These lamps could be worked only by very powerful 
currents, whereas with a lamp regulated by hand the 
voltaic arc could be obtained with weaker currents, giving 
of course a less intense light. 
3. They worked with regularity only when the current 
was constant, or varied within very restricted limits. 
I traced the cause of these defects to the fact that the 
working of the regulating mechanism was based upon a 
kind of equilibrium between the attractive force of an 
electro-magnet and the counteracting force of a spring. 
Such a system does not regulate the distance between the 
charcoal points, but only the general force of the current in 
the circuit. Now under these circumstances it is possible 
that, when two or more lamps are placed in series in a 
circuit, one of them may have its carbons in contact, whilst 
the carbons of the other lamp or lamps are at a greater or 
less distance apart, without the equilibrium Dettveen the 
electro-magnets and the counteracting springs being dis- 
turbed. 
Now it was to obviate this defect that I endeavored to 
devise an arrangement which, whilst allowing each lamp 
placed in a circuit to be independent of the general inten- 
sity of the current and its variations, would enable it to 
maintain constant the resistance of its own voltaic arc, and 
this arrangement appeared to me obtainable by applying to 
the regulator lamps the principle of the differential action of 
derived currents. 
It was in 1869 that I made the first experiment on the 
foregoing arrangement with a regulator lamp of M. Foucault, 
the counteracting spring of which I replaced by a supple- 
mentary electro-magnet traversed by a very weak deriva- 
tion of the current, parallel to the voltaic arc. This electro- 
magnet was wound with a wire of high resistance, and the 
current producing the voltaic arc passed through the other 
electro-magnet. The armatures of these electro-magnets 
were placed at the two extremities of a rocking-lever, 
carrying at its centre of oscillation an arm which controlled 
the mechanism for increasing or diminishing the dis- 
tance between the carbons ; and the rocking-lever was in 
equilibrium when the voltaic arc possessed its normal re- 
sistance. 
