348 
the deviation and dispersion required are large, the devia- 
tion amounting to over 300°; that is to say, the ray of 
light is bent through almost a complete circle ; the light 
from stars is dim, and many prisms cannot be employed 
to widen out the spectrum, but in the case of the sun, 
there is light sufficient to give us a bright spectrum after 
it has been enormously dispersed. 
Figs. 31 and 32 show a very powerful spectroscope to be 
attached to the telescope for observing the spectrum of 
the sun. One peculiarity of the instrument in Fig. 33 is 
that the ray of light having passed once through the 
lower part of the train of prisms, is received by a right- 
angled prism, which totally reflects the light twice, send- 
ing the ray of light back through the upper part of the 
same prisms, when it is again refracted ; we thus have, 
by using these prisms, the same effect as if thirteen 
prisms had been employed. The ray of light enters the 
Fig. 33.—Automatic arrangement for securing the minimum deviation of the 
observed ray. 
instrument by the lower tube, and after passing first 
through the lower half of the prisms, and back through 
the upper half, is received in the upper tube, and reflected 
upwards for convenience of observation. These prisms 
are so arranged, that whatever part of the spectrum is 
being observed, they are always at the angle of minimum 
deviation for this part of the spectrum, a very important 
point, as if this is not attended to the spectrum loses 
much of its brilliancy and sharpness. This is done either 
by attaching the prisms to a spring of ebonite or gun 
metal moving on a fixed point near the first prism of the 
series, as in the arrangement shown, or each prism may 
be attached to a radial bar acting on a central pin, as 
shown in Fig. 33. J. NORMAN LOCKYER 
(To be continued.) 
HUNTERIAN LECTURES BY PROF. FLOWER 
LECTURES IV. V. VI: 
I? will not be necessary in describing the fossil remains 
of mammalia to devote any time to the consideration 
of the Monotremata, for thoughit might have been supposed 
that these animals, the Echidna and Duck-bill, on account 
of their being the lowest in the scale, would have been 
largely represented in ancient times, evidence to that 
effect has not been forthcoming. In the post-pliocene of 
Australia, the lower end of the humerus of a large 
Echidna, was found by Mr. Krefft, curator of the Museum 
at Sydney, and that is apparently the only recorded 
specimen from the class. With regard to marsupial 
animals the case is very different, and the remains 
prove that their geographical distribution formerly was 
not at all what it is now, when they are confined 
NATURE 
. [Mar. 6, 1873 
to Australia, the Austro-malay Archipelago, and South 
America, The family may be classified by the teeth or by 
the feet. According to the former method the Kangaroos, 
Phalangers, Koalas, in which there are only two lower 
incisors, without persistent pulps, form one herbivorous 
group ; the Wombats a second ; and those with more than 
two lower incisors, including the Bandicoots, Dasyures, 
Thylacine, and Opposums, a third carnivorous section. 
If the structure of the feet be taken as the main point 
the tendency to the reduction of the second and third 
digits places the Bandicoots with the Kangaroos, instead 
of with the Dasyures, and does not otherwise modify the 
arrangement. The at first sight great difference between 
the molar teeth of the Thylacine and the pci can 
be easily biidged over by a comparison of intermediate — 
forms ; looking for instance at an upper molar in the 
latter, its crushing surface presents two broad ridges, 
with an intermediate depression, in which there is an 
oblique groove. In the Thylacine there is a central 
large, and two lateral smaller tubercles, with a band 
connecting the medium with one of them. There is also 
a small posterior and two very small anterior tubercles 
in the cingulum. In Perameles the molar presents two 
rows in a double crescent, in front of which are four 
minute processes, which represent those of the cingulum 
of the Thylacine, the crescents being representatives of 
the big tubercles. In the Kangaroo Rats the tubercles 
alone remain, and in the Kangaroo these blend to form 
the ridges. 
Respecting the fossil forms, those from the Purbeck — 
beds have been thoroughly worked out by Prof. Owen. 
With the exception of P/agzaulax they belong to the 
polyprotodont division, and nearly all have more than 
seven teeth of the molar series, Zyzconodon and Triacan- 
thodon being the exceptions, they also being peculiar and 
differing from all existing Marsupials in having four pre- 
molars and three molars. There is no evidence to show 
whether there was any succession of the teeth. Plagiau- 
fax has been the subject of one of the most important 
controversies in connection with paleontology, between 
Prof. Owen and the late Dr. Falconer, the former main- 
taining that it was carnivorous, eating the lizards found 
with it; Dr. Falconer that it was herbivorous and allied 
to Hypsiprymnus. The fact of its having only two lower 
incisors, and that the molars are hypsiprymnine in form 
tends to show that it must have had some relation to the 
herbivorous group, and shows that at so ancient a date 
ee family had already divided in the manner that we now 
nd it. 
The tertiary Marsupialia must next be considered. In 
the Eocene gypsum of Montmartre several small skeletons 
have been found, clearly referable to the Opossums, and 
with a similar dentition, from which Cuvier was able to 
classify them correctly and predict the existence of mar- 
supial bones in the uncovered skeletons, From Auvergne 
three similar ~ iocene species have been described, and 
in England Mr. Charlesworth has, on undoubtedly insuffi- 
cient evidence, referred a premolar to the same genus, 
Dideiphys. The Yale College expedition have obtained, 
among the large number of bones that they have col- 
lected, some which Prof. Marsh thinks are Marsupial. 
In the Pliocene there have not been any fossil remains of 
this sub-class yet obtained, but many in the Quaternary 
period. In the Brazilian caves Opossums have been 
found in abundance, and in the Wellington Valley and 
many other parts of Australia extremely interesting forms 
have been obtained, which must be referred to more 
fully. Prof. Owen has studied them in great detail. The 
remains may be divided into two divisions ; (1), those 
allied to existing genera ; and (2), those not now repre- 
sented. With regard to the former it is interesting to. 
observe that the Thylacine and Ursine Dasyure, now re- 
stricted to Tasmania, at one time abounded on the main- 
land, There are also remains of enormous Wombats and 
