ZOOLOGY AND BOTANY^ MICBOSCOPY, ETC. 29 



inclined to the horizontal. The position of the anus of Rusconi 

 affords still further proof of a " relative isotropy " ; it always appears 

 upon the white hemisphere, and is intimately connected with the 

 direction of the axes of the egg. 



The paper concludes with some observations on the development 

 of Marsilia made by Dr. H. Leitgeb ; it appears that in the embryo of 

 this plant, the position of the first divisional septum in every case 

 coincides with the axis of the archegonium ; it is, however, capable of 

 rotation round the latter, and as soon as the axis of the archegonium 

 ceases to be vertical, takes such a position that the embryo is divided 

 into an upper and lower half. 



The occurrence of the same principle of development in two such 

 widely different types is evidently an indication of its wide-spread 

 importance. 



Influence of Physico-Chemical Agencies upon the Development 

 of the Tadpoles of Rana esculenta.* — E. Yung subjected tadpoles just 

 hatched to the action of saline solutions of various strengths. The 

 salts employed were obtained by the evaporation of the water of the 

 Mediterranean, and the larvje were placed in solutions of 1, 3, 5, 7, 

 and 9 per 1000, which were renewed at the same time in all the 

 vessels, and the whole were in other respects placed under precisely 

 the same conditions. As a general result, M. Yung states that the 

 tadpoles are developed the more slowly the more considerable the 

 degree of saltness of the water. In the solution of 9 : 1000 no trans- 

 formation took place, though some tadpoles live long enough to 

 acquire hind limbs. In a solution of 10 : 1000 very young tadpoles 

 die in a few hours : elder ones survive for a few days. The author 

 remarks upon the importance of placing equal numbers of individuals 

 in each vessel in experiments of this kind, as their development is 

 found to be slower in proportion to the number living together. 



M. Yung also subjected young tadpoles, which normally live in 

 quiet water, to continuous agitation in a vessel containing two litres 

 of water regularly renewed and suitable food. Under these conditions 

 the eggs developed well ; but the newly hatched tadpoles, being too 

 feeble to seize their prey in so disturbed a medium, died of hunger, 

 unless care was taken to give them daily a few moments of repose to 

 take their food. If these tadpoles be compared, at different periods, 

 with others of the same brood developing in quiet water, it is found 

 that the developing of the former is slower, that they are less pig- 

 mented, which indicates bad nutrition, and, lastly, that their tails 

 are relatively more developed, especially in width, which is explained 

 by the greater use they are obliged to make of the organs in struggling 

 against the waves. 



Colours of Feathers. t — The colours of the feathers of birds are 

 of two kinds : (1) Objective, that is, colours caused by the presence of 

 definite pigment, or by structural peculiarities of the feather itself, or 



* Arch. Sci. Pliys. et Nat., x. (1883) p. 347. See Ann. and Mag. Nat. Hist., 

 xiii. (1884) p. 72. 



t Proc. Zool. Soc. Loud., 1882, p. 409. 



