49 o PHILOSOPHIC ZOOLOGY 



the existence of the individual, and (2) the existence of the 

 species. The greater part of the body, having more particu- 

 larly to do with (i), is conveniently termed the "soma" (Gk. 

 soma, body), and this is the bearer of germ-cells, some of which 

 are destined to grow into fresh individuals, and are therefore 

 concerned with (2). An " acquired " character is one which 

 comes into existence in the soma, as an accommodation to its 

 mode of life, i.e. as an individual adjustment to surroundings. 

 Here have to be considered the results*of " use and disuse " of 

 organs possessed by the individual. Let us take, for example, 

 some of the sea-snails which live between tide-marks, and are 

 accommodating themselves to breathing damp air as against 

 air dissolved in water. The gill or gills which are specially 

 concerned with the latter kind of breathing have less work to 

 do than in purely aquatic forms, and there is no reason to doubt 

 that they may therefore (as the result of partial "disuse") be 

 slightly diminished in size in the lifetime of an individual which is 

 migrating towards high-tide mark. On the other hand, the roof of 

 the gill-chamber (see vol. ii, p. 460) has to do with breathing damp 

 air, and in the lifetime of the individual supposed, may well (by 

 4 'use") acquire increased specialization in connection with that duty. 



According to the Lamarckian view, these two acquired char- 

 acters of the soma, i.e. dwindling gill and specializing roof to 

 gill-chamber, would be transmitted to the offspring. Were this 

 so, use and disuse might ultimately lead to the evolution of a 

 race of land-snails well adapted for air-breathing, but with gills 

 shrunk to mere vestiges or absent altogether. 



Lamarckism also involves the view that the surroundings of 

 an animal, by their direct action, bring about acquired char- 

 acters, positive or negative, as the case may be. We have, in 

 other words, a direct action of the environment. Considering 

 once more the case of a sea-snail living between tide-marks, it 

 may be regarded as alternately subject to two influences so far 

 as breathing is concerned, i.e. the action of the water which 

 covers it for part of its existence, and the action of the damp 

 air which surrounds it during the other part. The former 

 favours gill-retention, the latter gill-reduction, and conversely as 

 regards the arrangement for breathing ordinary air. Near low- 

 tide mark the influence of water is obviously predominant, and 

 near high-tide mark the action of air is more felt. 



