PROGRESS OF MICROSCOPICAL SCIENCE. 149 
specially worthy of study, the exposition of vegetable morphology 
therein given being such as only the expert botanist, who is at the 
same time deeply versed in physical science and minute anatomy, 
could have written. The whole work is a mine whose treasures 
might occupy many workers in developing. 
PROGRESS OF MICROSCOPICAL SCIENCE. 
The Structure of Centropyxis.—Professor Leidy, of U.S.A., who has 
been publishing a series of papers on the structure of Rhizopods and 
their cogeners before the Academy of Sciences of Philadelphia, gives 
the following description of this interesting genus :—“ Centropyxis is 
a nearly allied generic form to Arcella, and is so polymorphous that I 
have been puzzled to define varieties. The test or basis of the test is 
membranous, and appears not to exhibit the hexagonal structural 
elements of that of Arcella. The shape is a modification of that of the 
latter; the mouth and the summit of the dome being eccentric in 
opposite directions. The dome varies in degree of prominence, and is 
always convex. The mouth varies in proportionate size, and is more 
frequently sinuous at the border than completely circular. The test 
presents all the variations of colour presented by Arcella vulgaris. It 
is frequently provided with from two to five or more hollow, conical 
spines diverging from the wider border or that most distant from the 
mouth. Sometimes the test is clean or devoid of all adherent matters 
and appears homogeneous; mostly, however, it is more or less covered 
with mineral particles. Sometimes it is as completely covered with 
quartzose particles as an ordinary Difflugia, and frequently it is loaded 
with larger stones along the deeper border. In some specimens the 
test appears to be wholly composed of a single species of diatom 
shells. I have observed a peculiar point of structure in most tests of 
Centropyxis, which appears heretofore to have escaped notice. From 
the sinuous border of the mouth a number of processes extend upward 
to the dome. These are expanded at the end, and look as if intended 
to support the roof of the test, though I have not been able to satisfy 
myself that they actually reach it. Nor have I been able to ascertain 
whether the number of processes is constant, but they have appeared 
to me to vary in number from four to seven. They are not visible 
looking directly into the mouth of the test, but a glimpse of one or 
two may be detected when the mouth is aslant, as the test is made to 
turn towards one side. From the usual discoid form of the test it is 
not easy to retain it in position on edge to conveniently examine the 
processes, and when the test is observed with adherent sand they 
cannot be seen at all.” 
Bathybius come to life again !—This singular, at one time supposed 
animal organism, and which has since been relegated by Professor 
Huxley to the mineral world, has been, so to speak, resuscitated by 
