. The theory of evolution in the light of facts. o twelveeggs, which are enveloped in a parchment-like, yellowish-white, opaque shell, hke those which other Lizardspossess/ ^ With the Meadow Lizard {L. sera^pa) Kammerer has established the fact that thenormally parchment-like eggsbecome quite hard-shelled (andat the same time round) if theparents are kept permanentlyunder a temperature of 30° to35° C. (Fig. 46). If the lizardsbe restored to the normalcooler conditions, the firstgeneration lays still hard-shelled eggs; and also theyoung which are born undernormal conditions from the heat forms,
. The theory of evolution in the light of facts. o twelveeggs, which are enveloped in a parchment-like, yellowish-white, opaque shell, hke those which other Lizardspossess/ ^ With the Meadow Lizard {L. sera^pa) Kammerer has established the fact that thenormally parchment-like eggsbecome quite hard-shelled (andat the same time round) if theparents are kept permanentlyunder a temperature of 30° to35° C. (Fig. 46). If the lizardsbe restored to the normalcooler conditions, the firstgeneration lays still hard-shelled eggs; and also theyoung which are born undernormal conditions from the heat forms, which have be-come black by reason of thewarmth, still clearly show theblack coloration in the firstgenerations and, quite natur-ally, the more so the nearerthey approach the adult form. The very first stagesshow still clearly the hghter colouring. This example confirms in all points what we haveso far said regarding the influence of the external worldand the influencing of the embryonic stages ; it shows ^ Other — normal egg-laying c d 0 Fig. 46. — Thermal changesIN THE Meadow , normal animal; b, artificiallyblackened; c, normal egg; d,egg of first deposit in heat; e,hard-sheUed egg ex second andthird laying periods. {After Kammerer.) EMBKYOGENY . 213 also that there are many vacillations in the relationsof the intra- to the extra-uterine period of development. In the Alpine Salamanders we observe how aninternal stage can be omitted; in the Mountain Lizardthe contrary can be effected by experiment. (c) We will now assume that the causes which haveled to the said change in the Alpine Salamander con-tinued, and also increased in power, so that the inutilityof a constructed gill stage became ever greater. Weknow that in such cases a tendency immediately showsitself—and this is the case with all organisms—no longerto form such non-functional organs. The result willbe that at first a defective construction follows, untilfinally the former organ perhaps en
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