3214 Microscopical Society. 



illustrate this structure from the Medusae, the Hydra?, and especially from the Spiro- 

 stomaand the Stylonychia, polygastric animalcules; and his observations went to show 

 that the organization in this class of animals is exceedingly simple, consisting of little 

 more than a homogeneous fluid drawn out into spherical films or cells, probably in- 

 closing a very subtle vapour. 



A second paper, by H. C. Sorby, Esq., * On the Tensions developed among the 

 Tissues of Wood by its Growth,' was read. 



The author commenced by stating, that in studying the depolarizing structure of 

 wood, he had used as a polarizer a rotatable large Nichol's prism, placed behind the 

 lenses of the achromatic condenser ; and as an analyzer, a film of selenite and another 

 Nichol's prism, which could be rotated independently or conjointly, placed over the 

 eye-piece. By these arrangements, he obtained abundance of light when using high 

 powers ; and by rotating the selenite, the direction of the positively and negatively 

 doubly-refracting axes of the object under examination were easily ascertained. 



Upon examining with this apparatus longitudinal sections of recent wood, with a 

 power of about 400 linear, they were found to consist of laminae, some of which pos- 

 sess positive and others negative double refraction in the line of their length, the prin- 

 cipal axes lying one in that direction, and the other at right angles to it. This alter- 

 nation of positive and negative laminae, and the probable cause, form the principal 

 subjects of this paper. The number of alternations varies, but from five to ten are 

 usual. The passage from one to the other is often quite sudden, but is sometimes gra- 

 dual. The wood considered as the best for showing these effects, was that of the Co- 

 ni ferae ; and the effects of polarization, as exhibited by the medullary rays, the disks, 

 the spiral fibre, and the ducts, were described. The cause of alternation of the posi- 

 tive and negative laminae, is ascribed by Mr. Sorby to the tension produced by the 

 growth of the plant ; and he explains it by supposing that first of all the original walls 

 of the tubes of which the lamina? are composed were neutral, or had such a variable, 

 slight, positive and negative action as is seen in cellular tissue, and that then inside 

 them woody matter was deposited, which had a tendency to expand in the line of the 

 length. This, by stretching the original walls, would produce in them a positive ac- 

 tion in the line of their length, and their reaction on the fresh-formed tissue would 

 develope in it a negative structure ; and a constant repetition of this process would 

 produce the various alternations now under consideration. In conclusion, he stated 

 that although these suppositions might not adequately explain all the phenomena that 

 might be observed, still this structure proves that there have been alternations of lig- 

 neous tissue, either having tensions in different directions, or a self-existing double re- 

 fraction of different characters ; but he considers the supposition that the effects are 

 due to tension agrees with the neutral action of some parts and the general properties 

 of others much the best : and he felt convinced that the study of the double refraction 

 of the tissues of plants would be of great utility in arriving at a correct knowledge of 

 the manner of their development. 



Another paper, * On the Minute Structure of a Species of Fangasina,' by W. C. 

 Williamson, Esq., was also read. 



In former communications to the Society, the author pointed out the existence of 

 a curious system of tubes and canals, penetrating the parietes and septa of several spe- 

 cies of foraminiferous shells, in which the structure of Polystomella, some species of 

 Nonionina and Amphislegina were described. On making sections of a species of 

 Fangasina, If Orb., from Manilla, the existence of a much larger and more interesting 



