164 JOURNAL OF THE [junC, 



without a nucleus ; so that a nucleus seems to be essential to the 

 retention of the regenerative power of a cell. 



Dr. Gruber experimented in a similar manner upon Stenior 

 cceruleus. He observed that when this infusorian was divided 

 transversely through the centre, the posterior section in twelve 

 hours developed a new peristome-area with the large cilia and 

 the oral spiral. The part containing the mouth also added a new 

 posterior portion. A longitudinal division through the peristome 

 was followed by the same regenerative process, two complete 

 peristomes being again formed. — See Jour. Roy. Mic. Soc, 1S85, 

 p. 472. 



Choice of Objectives and Oculars. — Though objectives 

 of very high power are occasionally made, even xTirth-inch focus 

 being announced, the larger and more conservative portion of 

 microscopists evidently incline, as they always have done, toward 

 a much more moderate limit. It is probably quite safe to say 

 that objectives anywhere from kh to Tsth-inch, if not lower, can 

 now be obtained which will show, as well as has ever been done, 

 anything that has yet been seen by the microscope. 



The question as to the choice of moderate or extreme aper- 

 tures for objectives is still open, and somewhat evenly disputed. 

 Dr. Carpenter and a large following of conservative judges still 

 hold to the former view — not doubting the value of large aper- 

 ture, but believing that it should accompany higher powers, and 

 that to a I -inch, for instance, should not be assigned the aper- 

 ture and work of a ith, nor to a roths that of a ith; and this view 

 is corroborated by the mathematical computations of the relation 

 of aperture to power by Prof. Abbe (J. R. M. S., 1883, p. 790). 

 On the other hand, a large number of experienced persons prefer 

 large angles even for biological work, some claiming that the 

 highest attainable angles are the best for all uses and powers. 



In the combining of oculars with objectives, it is still unde- 

 cided whether it is preferable to secure a sufficient variety of 

 powers by means of a large number of objectives, or by the high 

 and low eye-piecing of a few. Dr. Carpenter prefers the 2-inch, 

 and would use even the i-inch for exceptional purposes. Prof. 

 Abbe selects Ids-inch (X 15) as the highest really useful ocular. 

 — R. H. Ward, M. D. Appletons Annual Cyclopedia for 1S84 .• 

 Article, Microscopy. 



