732 SUMMARY OF CURRENT RESEARCHES RELATING TO 



7. General. 



Protoplasmic Movements and their Relation to Oxygen Pressure.* 

 — Mr. J. Clarke has made a long series of experiments in order to 

 ascertain the minimum pressure of oxygen necessary to restore the 

 streaming, amoeboid, and ciliary movements of protoplasm after they 

 have come to rest in the absence of that gas. The minimum for the 

 streaming movement in the plasmodia of Myxomycetes, and in the cells of 

 hairs and other tissues was found to vary from 1 mm. to over 3 mm. 

 With the vegetable cells the variation was much more extensive. The 

 age of the cell, and the conditions under which it has been developed, 

 influence to some extent the minimum oxygen pressure necessary to 

 restore movement. The time taken by the protoplasm to recover its 

 streaming movement is too short to be measured in cases where the 

 conditions are favourable, but increases as the cell-wall thickens, or the 

 cell ages, or as the length of time between the cessation of movement 

 and the introduction of the necessary oxygen supply. After ciliary 

 movement is arrested in any healthy infusorian by the absence of oxygen 

 the organism soon begins to disintegrate. The introduction of an 

 oxygen supply of about 1 mm. is sufficient to arrest disintegration and 

 restore ciliary movement, provided the breaking-up has not proceeded 

 too far. The growth of the plant, and the streaming of proto^^lasm in 

 the active cells thereof appear to be parallel phenomena ; streaming, or at 

 least the power of very rapidly assuming the streaming movements, 

 is possessed by the parenchyma and, probably, the phloem of plants 

 so long as they continue to grow in an atmosphere of hydrogen. 

 Inability on the part of the protoplasm to continue these movements, 

 seems to be always associated with total cessation of growth. 



Orientation of Animals towards Light.f — Herr J. Loeb has made 

 some observations on " animal heliotropism," from which he concludes 

 that the same luminous stimuli as we consider to produce sensations in 

 ourselves affect all, and even the lowest eyeless animals, and this not- 

 withstanding the great differences in the development of specific helio- 

 tropic organs. The differentiation of tliese organs has, therefore, been 

 due to the fact that the laws of luminous stimulation remain unaltered. 

 Their influence must be due to a fundamental peculiarity of living 

 matter. 



Orientation of Animals towards Gravity. | — The same author dis- 

 cusses also the phenomena of " animal geotropism " ; he thinks it highly 

 probable that the muscular vibrations are of importance for orientation 

 in space, but he proposes to extend his inquiries. 



B. INVERTEBRATA. 



Zoology of Victoria.§ — The eighteenth decade of this work edited 

 by Prof. M'Coy contains figures and descriptions of a number of Polyzoa, 

 and of the Great Eed King-Crab (Pseudocarcinus gigas). The male of 

 this crab is much larger than the female, having a carapace nearly a 

 foot in width, and is provided with immense powerful pincers. The 

 descriptions of the Polyzoa are, as before, drawn up by Mr. M'Gillivray, 



* Proc. Eoy. Soc, xlvi. ri889) pp. 370-1. 



t SB. Physik. Med. Gesell. Wurzburg, 1888, pp. 1-5. % T. c, pp. 5-10. 



§ ' Proclromus of the Zoology of Victoria,' xviii. (1889) pp. 171-80. 



