SCIENTIFIC SUMMARY. 
337 
by cementing laminae of selenite of different thicknesses (varying from 
2^0 to ^ of an inch) between two plates of glass. Invisible under 
ordinary circumstances, they exhibit, when examined in the usual polarising- 
apparatus, the most brilliant colours, which are complementary to each 
other in the two rectangular positions of the analyser. Regarded in the in- 
strument which he has described, the appearances are still more beautiful ; 
for, instead of a single transition, each colour in the picture is successively 
replaced by every other colour. In preparing such pictures it is necessary 
to pay attention to the direction of the principal section of each lamina 
when different pieces of the same thicknesses are to be combined together to 
fbrm a surface having the same uniform tint ; otherwise in the intermediate 
transitions the colours will be irregularly disposed. 
ZOOLOGY AND COMPARATIVE ANATOMY. 
Ceratodus a Genus of Ganoid Fishes. — Dr. Albert Guthrie has sent a paper 
to the Royal Society descriptive of this curious fish, which has lately been 
discovered in Australia. It seems to be a species of ganoid fish, not very 
unlike the well-known Lepidosiren. After describing the various points of 
its anatomy in detail, the author of this important paper draws the follow- 
ing conclusions. 1. That Ceratodus and Lepidosiren (. Protopterus ) are more 
nearly allied to each other than to any third living fish, the latter genus 
diverging more towards the Amphibians than the former. 2. That the 
difference in the arrangement of the valves of the bulbus arteriosus cannot 
longer be considered of sufficient importance to distinguish the Dipnoi as a 
sub-class from the Ganoidei', but that the Dipnoi may be retained as a sub- 
order of Ganoidei. 3. That the sub-order Dipnoi may be characterised as 
Ganoids with the nostrils within the mouth, with paddles supported by an 
axial skeleton, with lungs and gills and notochordal skeleton, and without 
branchiostegals. 4. That a comparison of Teleostei, Chondropterygii, and 
Ganoidei shows that the two latter divisions, hitherto regarded as sub- 
classes, are much more nearly allied to each other than to the Teleostei , 
which were developed in much more recent epochs ; and therefore that they 
should be united into one sub-class — Palceichthyes — characterised thus : heart 
with a contractile bulbus arteriosus ; intestine with a spiral valve $ optic 
nerves non-decussating. 
The Sub-axial Arches in Man. — These form the subject of a very elaborate 
paper presented to the Royal Society by Mr. G. W. Callender. The author 
appears, so far as we can see, to admit Owen’s division of the cranial ver- 
tebrae, but imagines that two or more are essential parts. This paper shows 
considerable knowledge of the subject, but, so far as we can see, it is open 
to very serious objections. The paper will be found in abstract in the 
“ Proceedings of the Royal Society ” (March), and will be read with interest. 
Experiments in Pangenesis. — Mr. F. ^Galton, F.R.S., has undertaken a 
series of experiments which he thinks render it impossible to accept Mr. 
Darwin’s doctrine of pangenesis. These consisted in breeding from rabbits of 
a pure variety, into whose circulation blood taken from other varieties had 
