ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
325 
state of affairs in Ganoids. His chief result is that the cartilaginous and 
bony Ganoids are, like the Anura, without an intercuticular sheath. 
Thus they differ essentially from Elasmobranchs, Dipnoi, and Urodela, 
in which the intercuticular sheath is present. 
Development of Kidneys in Sturgeon.* — Dr. H. F. E. Jungerscn 
communicates some observations on the development of the kidneys in 
Acipenser sturio, in regard to which there is a lack of definite informa- 
tion. His most important result appears to be that the pronephros, 
which extends over five to six segments, has numerous funnels, but only 
one capsule and one glomerulus. It is thus more primitive than that of 
Lepidosteus, and shows a considerable resemblance to that of Amphibian 
larvae. 
Bibliography of Vertebrate Embryology.^ — Mr. C. S. Minot has 
prepared a list of 3555 papers dealing with this subject, and he has, he 
says, brought together about seven times the number of titles found in 
any previous bibliography of the subject, known to him. “ Nevertheless 
it is far from complete.” It will, however, be of great service, and may 
well be the foundation for a more perfect bibliography. The titles are 
grouped under subjects, which are arranged alphabetically, and there is 
an index of authors. 
/3. Histolog-y. 
Minute Structure of Nerve-centres.:]: — Prof. Ramon y Cajal, in his 
Croonian lecture, reminded his hearers that Golgi, who was the first to use 
the silver impregnation method, showed that the protoplasmic expansions 
of nerve-cells terminate by free extremities in the grey matter, and that 
the prolongations of the nerve-cells give off in their course through the 
grey matter very fine ramifying collateral branches ; Cajal has shown that 
axis-cylinders, in addition to their protoplasmic prolongations, end freely 
in the grey substance. His investigations do not admit of his allowing 
the sharp difference noted by Golgi between sensory and motor cells ; 
for example, in the olfactory bulb and retina there are cells which are 
morphologically motor, and others which are sensory ; it is clear, there- 
fore, that the function of a cell cannot be deduced from its shape and 
mode of branching. 
The grey matter of the spinal cord, in addition to commissural, con- 
necting and motor cells, has others which are called “ pluricordonal,” as 
in them a complex axis-cylinder furnishes two, three or more medullated 
fibres in connection with the columns of one side or of both. 
After entering into numerous details the lecturer expressed his belief 
that mental activity is not able to improve the cerebral apparatus by 
augmenting the number of cells, for the nervous elements lose their 
power of dividing during embryonic life ; it is, however, probable that 
intellectual exercise may produce in certain regions of the brain a large 
development of the protoplasmic apparatus, and of the system of nervous 
collaterals, so that associations already existing between certain groups 
of nerve-cells would be perfected by a further development of terminal 
twigs, of protoplasmic endings, and of nervous collateral branches, while 
* Zool. Anzeig., xvi. (1893) pp. 464-7, 469-72 (1 fig.). 
f Mem. Boston Soc. Nat. Hist., iv. (1893) pp. 487-614. 
X Nature, xlix. (1894) pp. 464-6. 
