H, J. Clark on the Microscope. 45 
sharks, are very thin-walled, hyaline, globular vesicles, each one 
of which contains a more or less darkened mesoblast, and within 
the latter are a certain number of entoblasts (nucleoli). Now 
under the least pressure, the cell-wall bursts quickly, and the 
mesoblast becomes fissured or wrinkled. In this condition the 
no less careful an observer than Johannes Miiller. Now in the 
turtle, at least, the mesoblast bade self-division until there 
are innumerable mesoblasts in the parent cells; and after the 
latter have congregated to ae the different layers of the incip- 
ient organs of the embryo, and burst, the former unite side by 
side, and thus become the original cells of the young tissues. 
I feel that I cannot urge too strongly the utmost necessity of 
studying living beings as nearly in a state of nature as is possi- 
ble; to attempt this by all available means and contrivances, 
and, a ve all, patiently, not begrudging the time, because more 
numerous observations might be obtained by making a piece- 
meal and hurried show of dismembered Nat 
It would certainly be more profitable as tr as living beings 
are concerned, if the whole world of science should, for a while 
which cae the dissecting-knife. The first ge been in- 
ae een eT es 
ded, because 
ered as high authority both in England and in thi 
have attempted to depreciate the value of the flat field ca om 
angle of aperture in the study of living objects. This is a little 
remarkable, since it comes from a country where, until recently, 
the most finished microscopes of this kind were made, and where 
they are now to be found in large numbers. I will Tead a cost 
passages, which may be found on page 196 of Dr. Corpeidee 
work on the microscope. He says: 
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“The author feels it the more important that he should express himself 
clearly ~e strongly on this subject, as there is a great tendency at 
ese 
at the attainment of that ‘resolving power’ which is given by angular 
aperture, as the oy thing needful ; those other attributes which are of far 
more importance in almost every kind of scientific investigation, being 
comparatively little thought of ; and he therefore ventures here to repeat 
the remarks he e made u upon this subject, in his recent Presidential address 
to the Microscopical Society, of the correctness of which he has been 
