the Distinctive Characters in Amoeba. 143 



In the first place, no such permanent orifice can be detected 

 even with the aid of the highest powers of the microscope and 

 every essential accessory in manipulation. I am aware that this 

 may be regarded as inconclusive by some persons ; but, whilst I 

 am quite as ready as Mr. Carter to believe that our optical ap- 

 pliances frequently fail, even under the most favourable circum- 

 stances, to resolve extreme subtleties of organic structure, I con- 

 ceive that, in the example under notice, this evidence is not of 

 the purely negative character that it would be were no trace dis- 

 cernible of the process whereby the contents of the contractile 

 organ, or the effete matter within the food-vacuoles, are extruded 

 at the surface. 



The excretory aperture is extemporized, and its closure takes 

 place from within outwards, solely because the indefinite conso- 

 lidation of the sarcode, to which the name of ectosarc has been 

 very appropriately given by Dr. T. Strethill Wright, being at 

 its maximum at the immediate surface in contact with the 

 medium around, and decreasing in degree from the surface in- 

 wards, the same cause that prevents the coalescence of the 

 pseudopodia of Amoeba under ordinary circumstances, in the 

 first place increases the resistance to the passage of the object 

 about to be extruded as the surface is approached, and, in the 

 second, causes the coalescence to take place from within out- 

 wards, and its rate to depend upon the degree of consolidation 

 attained by the ectosarc (see p. 132). Hence (and this is a most 

 important fact), whilst the viscidity of the endosarc, when an 

 Amoeba is suddenly torn across, enables foreign bodies to slip 

 out as they do from a globule of oil (that is to say, without 

 driving a layer of the substance before them as they escape, or 

 leaving a depression on the surface behind them), the compara- 

 tive rigidity of the ectosarc causes a generally infundibuliform 

 tubule* or pit to be formed, which tubule or pit coalesces from 

 its inner pointed extremity in the direction of the exterior, and, 

 finally, becomes altogether obliterated. In the least active con- 

 dition of Amoeba villosa, when several villi frequently combine 

 to form single larger ones, the latter are often so hyaline as to 

 render the detection of anything like a canal inevitable, did it 

 exist ; and it is in these that the mode of formation of the ex- 

 cretory tubule and its closure can be so clearly made out as to 

 leave no doubt on the subject ; for as the point of the tubule 

 slowly advances outwards it leaves behind it a perfectly hyaline 

 tract, the appearance presented during the process of closure 

 being precisely similar to that observable in a thermometer- stem 



* See my observation on the infundibuliform tubule in the ' Annals ' for 

 May 1863, pp. 366, 367. 



