200L0GY AND BOTANY, MICROSCOPY, ETC. 927 



pressure is quite sufficient to make a deep depression on tlie whole of 

 the surface covered by these cilia, and it is on this surface that the 

 elongated peristome, which is characteristic of the Param:^cia, gradually 

 becomes hollowed out. This depression once produced and retained for 

 a sufficiently long time is preserved of itself ; as the ventral cilia work 

 throughout the whole of the life of the Paramecium more than the rest, 

 this buccal depression is assured for ever. As the cilia of the anterior 

 part work much more than those of the posterior, there is a mUch greater 

 pressure on the first half than on the second, and the former, therefore, 

 appears more compressed. To convince oneself of the truth of these 

 generalizations, it is only necessary to make use of a reagent which stops 

 the work of the cilia and causes the contents of the cell to swell out. 

 Under the influence of such a reagent, e.g. a faint odour of ammonia, 

 water penetrates rapidly into the Paramsecium and equalizes its walls. 

 The creature at once returns to the form under which it commenced its 

 existence, and becomes completely rounded. 



The author considers that the " law of heredity " must yield to the 

 physico-mechanical cause which underlies it. 



Action of the Environment.* — Mr. J. Arthur Thomson gives a sum- 

 mary of the influence of the environment upon the organism. The 

 paper is mainly an appendix to Semper*s ' Animal Life,' and an expan^ 

 sion of Spencer's conclusion that "the direct action of the medium was 

 the primordial factor in organic evolution." The author first furnishes 

 a tabular analysis of the external factors, and a classified review of 

 typical concrete researches. He proceeds to discuss the physiological 

 classification of the results, the variable susceptibility to environmental 

 influence, the different degrees and periods of environmental action, and 

 the like. The relation of environmental modification to heredity and to 

 "functional" and "organismal" variations are then referred to. In 

 conclusion the author summarizes the history of opinion in regard 

 to the action of the environment as a factor in organic evolution. This 

 " balance-sheet of representative facts and opinions in regard to environ- 

 mental modification " is backed up by a copious bibliography. 



Elimination and Selection.! — Prof C. Lloyd Morgan suggests the 

 use of the term " Natural Elimination " alongside of " Natural 

 Selection." " Variations," he says, " are subjected to a double process 

 — a process of elimination- — weeding out the unfit ; and a process of 

 selection — choosing out the more fit. Of these, elimination is the more 

 universal, selection only coming into play when intelligence has definitely 

 appeared on the scene of life. Of the three kinds of variations — favour* 

 able, neutral, and unfavourable — elimination only gets rid of the 

 unfavourable, leaving both favourable and neutral in possession of the 

 field, except where severe and long-continued competition has rendered 

 even the neutral variations relatively unfavourable. Selection, on the 

 other hand, picks out only the favourable variations ; so that under 

 selection alone, the occurrence of useless structures and features would 

 be anomalous. Both principles have been operative under Nature ; and 

 both are included under Mr. Darwin's terms, " Natural Selection " and 

 " Sexual Selection." 



* Proc. E. Phys. Soc. Edin., ix. (1S88) pp. 446-99. 

 t Proc. Bristol Nat. Soc, v. (^1888) pp, 13, 



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