276.  Consult ‘Ueber die Vererbung,’ Jena, 1883; ‘Die Kontinuität des Keimplasmas,’ Jena, 1885; ‘Ueber die Zahl der Richtungskörper und über ihre Bedeutung für die Vererbung,’ Jena, 1887. These papers are translated as the second, fourth and sixth Essays in the present volume.

277.  See the second Essay.

278.  [See R. Meldola in Ann. and Mag. Nat. Hist., 1878, vol. i. pp. 158-161. The author discusses many cases among insects in which instinct is related to protective structure or colouring: he also considers that instinct is to be explained by the principle of natural selection which accounts for the other protective features.—E. B. P.]

279.  [See ‘Nature,’ vol. 36, pp. 491-507.—E. B. P.]

280.  [See ‘The Factors of organic Evolution’ in ‘The Nineteenth Century’ for April and May 1886.—E. B. P.]

281.  See ‘Biol. Centralbl.’ Bd. VII. No. 23.

282.  See the next Essay (VIII).

283.  Detmer, ‘Zum Problem der Vererbung,’ Pflüger’s Archiv f. Physiologie, Bd. 41, (1887), p. 203.

284.  [Dr. Weismann is here alluding to experiments upon the larvae of Rumia Crataegata. A short account of the results will be found in the Report of the British Association at Manchester (1887), and in ‘Nature,’ vol. 36, p. 594. I have now obtained similar results with many other species (see Trans. Ent. Soc., Lond. 1888, p. 553); but many of the results are as yet unpublished.—E. B. P.]

285.  [See the editorial notes by Raphael Meldola, in his translation of Weismann’s ‘Studies in the Theory of Descent’ (the Essay on ‘The Origin of the Markings of Caterpillars,’ pp. 241 and 306): also E. B. Poulton, in ‘Proc. Roy. Soc.,’ vol. xxxviii. pp. 296-314; and in ‘Proc. Roy. Soc.,’ vol. xl. p. 135.—E. B. P.]

286.  [Professor Meldola first called attention to the scattered instances of the kind here alluded to by Professor Weismann, in 1873: see ‘Proc. Zool. Soc.,’ 1873, p. 153. The author explains the relation of this ‘variable protective colouring’ to other protective appearances, and he is strongly of the opinion that the former as well as the latter is to be explained by the action of the ‘survival of the fittest.’

The validity of Dr. Weismann’s interpretation of these effects as due to adaptation, through the operation of natural selection, is conclusively proved by the following facts. The light reflected from green leaves becomes the stimulus for the production of dark brown pigment in those cases in which the leaves constitute the surroundings for many months. Under these circumstances the leaves of course become brown at a relatively early date, and protection is thus afforded for the remainder of the period, although the dark pigment is produced before the change in the colour of the leaf. Instances of this kind are seen in the colours of cocoons spun among leaves by certain lepidopterous larvae (see ‘Proc. Ent. Soc. Lond.,’ 1887, pp. l, li, and 1888, p. xxviii), the cocoons of the same species being of a creamy white colour when spun upon white paper.

Conversely, the light reflected from the same surfaces serves as the stimulus for withholding pigment in the cases alluded to by Dr. Weismann (larvae of R. Crataegata, &c.), in all of which the organism only remains in contact with the leaves while they are green, viz. at a time when the dark colour would be disadvantageous.

Hence precisely opposite effects are produced by the operation of the same force; the nature of the effect which actually follows in any case being solely determined by the advantage afforded to the organism.—E. B. P.]

287.  Compare Sachs, ‘Lectures on the Physiology of Plants,’ translated by H. Marshall Ward, p. 710.

288.  Compare Biol. Centralbl. Bd. VII. No. 21.

289.  I have used the expression ‘transient’ (‘passant’) in the same sense as ‘acquired,’ in order to enforce the conclusion that they are merely temporary, and disappear with the individual in which they arise. Since the characters of which Hoffmann speaks are hereditary, the term cannot be rightly applied to them, and I shall prove later on that they cannot be regarded as acquired characters in the sense required by the theory of descent.

290.   Compare a paper by J. Orth, ‘Ueber die Entstehung und Vererbung individueller Eigenschaften,’ Leipzig, 1887. This author considers my theory of the non-transmission of acquired characters to be incorrect, because he will insist upon using the term ‘acquired’ for those characters which are due to spontaneous changes in the germ; although he considers that they are only indirectly acquired. He also reproaches me with not having discriminated with sufficient clearness between the two modes in which new characters are acquired by the body, and with having altogether failed to take into account the class of characters which are due to variations in the germ. On the very same page he quotes the following sentence from my writings:—‘Every change of the germ-plasm itself, however it may have arisen, must be transmitted to the following generation by the continuity of the germ-plasm; and hence also any changes in the soma which arise from the germ-plasm must be transmitted to the following generation.’ Not only does the transmission of Orth’s ‘indirectly acquired characters’ necessarily follow from this sentence, but it is even distinctly asserted by it. I cannot understand how any one who is aware of what happened at the meeting of the Association of German naturalists at Strassburg in 1885, can charge me with the confusion of ideas which has prevailed since Virchow took part in the discussion of this question.

291.  His, ‘Unsere Körperform,’ Leipzig, 1874, p. 58.

292.  Compare on this point Nägeli in his ‘Theorie der Abstammungslehre.’ This writer also concludes from similar facts that external influences have wrought in the idioplasm, changes which were at first ineffectual, and which only increased during the course of generations up to a point at which they could produce visible changes in the plant. He does not, however, draw the further conclusion that these changes only influence the germ-plasm, for he was not aware of the distinction between germ-plasm and somatoplasm.