The President'' s Address. By the Bev. W. H. Dallinger. 197 



the N.A., and the great gain in delicate results derivable from 

 collar-adjustment. 



Mr. T. Powell has constantly and in a con amove and laborious 

 way, responded to my thirst for this enlargement of N.A. A 1/25 

 and a 1/50 with N.A. 1 • 38 were a triumph of some three years 

 ago, accomplished at my earnest request. But in going over the 

 best results attained by all my preceding lenses, I was able to 

 see how much they were transcended by these beautiful instru- 

 ments ; that is to say, how much more clearly and certainly the 

 more hidden and delicate results on which I had worked so long 

 were attained, and how much more easy it was by their use to 

 follow out the unknown and most difficult details which I had at 

 this time begun to fafrly grapple with, in the nuclear bodies of 

 these minute organisms, and once more I used personal and dele- 

 gated influence to obtain from Mr. Powell, if possible, a still greater 

 NA. The result is that I have received during the year just 

 expired not only the 1/6 with a N.A. of 1*5, but also a 1/12 

 and a 1/20 of precisely the same N.A. 



Now all the results I am about to record have been attained by 

 these higher class lenses ; and every point of detail, and disclosure 

 of structure, has been either more or less largely indebted, or wholly 

 due to the latter, and above all to the latest of these object-glasses. 



The larger proportion of the septic organisms whose life- 

 history we have thoroughly studied, were distinctly nucleated 

 bodies. I know of no clear reason for concluding that they 

 are either vegetal or animal ; they possess in fact some of the 

 characteristics of both, and certainly they represent the lowliest 

 organization of either great line of organic life. Since the nuclei 

 of such lowly and minute organisms would be likely to present 

 nuclear phenomena in their simplest condition, and since from a 

 complete knowledge of the history of the forms, there would be no 

 difficulty in correlating nuclear with general somatic changes, I 

 determined to do to the utmost what I could do in the study of 

 any discoverable changes in these nuclei. The four forms selected 

 for study are shown by plate VII. figs. 1-4. These are copies of my 

 original drawings presented to this and the Eoyal Society between 

 1873 and 1875. The presence of the nucleus is sufficiently 

 manifest in each, indicated by the letter n ; but the certainty of 

 this being such was found in the fact, that in all instances of fission, 

 an act constantly repeated by each form and by a long succession 

 of them, the nucleus from the first to the last stage in the act of 

 cleavage, took part, and was itself entirely divided. That which 

 greatly perplexed us in constant observation in the earlier researches 

 on these forms was the origin of this nucleus. We were never 

 certain when, in the growth of the organism from the germ, it 

 actually arose, nor how it first made its appearance. 



