116 Transactions of the Society. 



alumina and lime. If the optician were supplied with fresh sub- 

 stances possessing the requisite properties, we might not only have 

 objectives of more perfect corrections, but higher powers with flatter 

 curves and larger lenses. 



Passing from objectives to their employment and performance, 

 we find Professor Abbe dealing with the conditions necessary for 

 the resolution of close-lined and analogous objects, Mr. Dallinger 

 measuring the flagella oi Bacterium termo and finding them less than 

 the 200,00Uth of an inch, and Dr. Pigott exhibiting, by remagnifi- 

 cation, the image of a spider line diminished to the one-millionth of 

 an inch. 



If we consider the application of high powers to natural history, 

 it is an interesting question how far the existing optical means 

 enable the structure and rank of many of the minuter organisms to 

 be discovered, and how far down in the scale sexual generation can 

 be affirmed, or, with probability, assumed. 



Professor Haeckel places amongst his Protista, eight classes 

 of creatures, including Amoeba, Flagellata, Diatoms, &c., and 

 affirms of the whole list " that the most important physiological 

 characteristic of the kingdom Protista lies in the exclusively non- 

 sexual propagation of all the organisms belonging to it." * With 

 regard to this statement, it may be mentioned that in 1863 Dr. 

 Wallich published a remarkable series of observations on the form 

 of Amoeba he discovered in a Hampstead pond, and named villosa 

 from its having a permanent villous organ protruding from one 

 part. He stated that " one of the most remarkable amongst the 

 most novel and varied characters of the Amoebae consists in the 

 vesicle, in which the true nucleus is contained, having been found 

 to be distinctly membranous in some individuals." He noticed 

 also " a clear nucleolus," and inquired whether the appearances 

 presented justified the belief that the creature possessed " a germ 

 cell and sperm cells." t 



In April, 1875,1 Messrs. Dallinger and Drysdale described a 

 series of facts in the life-history of certain flagellate monads, includ- 

 ing a sexual union, a division of nucleus, and formation of germs at 

 first so minute as to be separately invisible, and then developing by 

 several changes into the parental form. A magnification of 2600 

 diameters sufficed for watching these processes, and made the nuclei 

 appear about one -eighth of an inch in their shortest diameter. One 

 of the creatures in its most globular condition had, with that power, 

 an apparent longest diameter exceeding one inch, and the shorter 

 diameter a httle under an inch. If we compare these dimensions 

 with those of Bacterium termo magnified 4000 diameters, in Mr. 



* ' History of Creation,' vol. ii. p. 69. 

 t ' Ann. N. H.,' May, 1863. 

 X ' M. M. J.,' May, 1875. 



