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PROGRESS OF MICROSCOPICAL SCIENCE. 
The Development of the Sturgeon. — In a late number of tlie ‘ Bulletin 
of the Acclimatization Society of Paris’ there is an account of the 
sturgeon’s reproduction (sturgeon of the Volga), by Professor Ows- 
jannikow. It seems that the sterlet ( Acipenser ruthenus ), the smallest 
of the Russian sturgeons, spawns in the Volga early in May on rocky 
bottoms, the temperature of the water being at 10° R. ( = 54^° F.). 
The eggs are readily fecundated by the artificial method. After they 
have been in the water a few minutes they adhere to any object which 
they touch. The development of the embryo can be observed in pro- 
gress at the end of one hour. On the seventh day they hatch. At 
first the young fish are 0 m, 007 (about inch) long. At the age of 
ten weeks they are nearly two inches long. They feed on larvae of 
insects, taking them from the bottom. Both in the egg and when 
newly hatched, the sterlet has been taken a five days’ journey from the 
Volga to Western Russia, and in 1870 a lot of the eggs were carried 
to England to stock the river Leith. This species passes its whole 
life in fresh water. The other species inhabiting the Baltic, Acipenser 
sturio, A. Huso , A. stellatus, and A. Giildenstddtii, are anadromous. 
These species hybridize, and freely, and from this circumstance some 
Russian savants have pronounced them only varieties instead of 
species. 
The Stomata of Leaves are well described for a couple of species in 
the £ American Naturalist,’ by Professor T. D. Biscoe. In studying 
the development of these complex organs, he takes the youngest leaf 
of the plant, and finds on its base (the youngest portion) no trace or 
hint of stomata. A very little higher up he finds the epidermis ap- 
pearing, many of the cells having built a partition across their front 
end, cutting off about a quarter of the original cells. These small 
cells are distinguished from the remaining portion of the originally 
single cells, and from the undivided cells, by being filled full of 
granular protoplasm, while the other cells are only partially filled with 
the protoplasm constituting the nucleus. These little cells, called 
mother cells, soon grow so as to become longer than broad, and are 
raised by the more rapid growth of the surrounding cells so as to leave 
an air-space below. An approach to a spherical form is now made by 
the mother cells, and the walls of the neighbouring cells are a little 
thickened with the deposition of cork substance giving the first trace 
of the thick-walled square of the ripe stomata. Next the mother cell 
divides by the formation of a thin partition which runs in the direction 
of the point of the leaf, and is perpendicular to its surface. Soon this 
partition thickens in the middle, and splits through the thickened 
portions to within about a fifth of each end. All further growth only 
effects minor changes in the form of the cells, or an increased thicken- 
ing of their wall. 
The Structure of Graptolites. — Professor Allman, in a recent paper* 
“ Annals of Natural History,” May, deals with the affinities of these 
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