The Evolution of Man — Volume 2

Chapter 2.30. Results of Anthropogeny.

LIST OF ILLUSTRATIONS.

FIGURE 2.210. THE LANCELET.

FIGURE 2.211. SECTION OF THE HEAD OF THE LANCELET.

FIGURE 2.212. SECTION OF AN AMPHIOXUS-LARVA.

FIGURE 2.213. DIAGRAM OF PRECEDING.

FIGURE 2.214. SECTION OF A YOUNG AMPHIOXUS.

FIGURE 2.215. DIAGRAM OF A YOUNG AMPHIOXUS.

FIGURE 2.216. TRANSVERSE SECTION OF LANCELET.

FIGURE 2.217. SECTION THROUGH THE MIDDLE OF THE LANCELET.

FIGURE 2.218. SECTION OF A PRIMITIVE-FISH EMBRYO.

FIGURE 2.219. SECTION OF THE HEAD OF THE LANCELET.

FIGURES 2.220 AND 2.221. ORGANISATION OF AN ASCIDIA.

FIGURES 2.222 TO 2.224. SECTIONS OF YOUNG AMPHIOXUS-LARVAE.

FIGURE 2.225. AN APPENDICARIA.

FIGURE 2.226. Chroococcus minor.

FIGURE 2.227. Aphanocapsa primordialis.

FIGURE 2.228. PROTAMOEBA.

FIGURE 2.229. ORIGINAL OVUM-CLEAVAGE.

FIGURE 2.230. MORULA.

FIGURES 2.231 AND 2.232. Magosphaera planula.

FIGURE 2.233. MODERN GASTRAEADS.

FIGURES 2.234 AND 2.235. Prophysema primordiale.

FIGURES 2.236 AND 2.237. Ascula of Gastrophysema.

FIGURE 2.238. Olynthus.

FIGURE 2.239. Aphanostomum Langii.

FIGURES 2.240 AND 2.241. A TURBELLARIAN.

FIGURES 2.242 AND 2.243. Chaetonotus.

FIGURE 2.244. A NEMERTINE WORM.

FIGURE 2.245. AN ENTEROPNEUST.

FIGURE 2.246. SECTION OF THE BRANCHIAL GUT.

FIGURE 2.247. THE MARINE LAMPREY.

FIGURE 2.248. FOSSIL PRIMITIVE FISH.

FIGURE 2.249. EMBRYO OF A SHARK.

FIGURE 2.250. MAN-EATING SHARK.

FIGURE 2.251. FOSSIL ANGEL-SHARK.

FIGURE 2.252. TOOTH OF A GIGANTIC SHARK.

FIGURES 2.253 TO 2.255. CROSSOPTERYGII.

FIGURE 2.256. FOSSIL DIPNEUST.

FIGURE 2.257. THE AUSTRALIAN DIPNEUST.

FIGURES 2.258 AND 2.259. YOUNG CERATODUS.

FIGURE 2.260. FOSSIL AMPHIBIAN.

FIGURE 2.261. LARVA OF THE SPOTTED SALAMANDER.

FIGURE 2.262. LARVA OF COMMON FROG.

FIGURE 2.263. FOSSIL MAILED AMPHIBIAN.

FIGURE 2.264. THE NEW ZEALAND LIZARD.

FIGURE 2.265. Homoeosaurus pulchellus.

FIGURE 2.266. SKULL OF A PERMIAN LIZARD.

FIGURE 2.267. SKULL OF A THEROMORPHUM.

FIGURE 2.268. LOWER JAW OF A PRIMITIVE MAMMAL.

FIGURES 2.269 AND 2.270. THE ORNITHORHYNCUS.

FIGURE 2.271. LOWER JAW OF A PROMAMMAL.

FIGURE 2.272. THE CRAB-EATING OPOSSUM.

FIGURE 2.273. FOETAL MEMBRANES OF THE HUMAN EMBRYO.

FIGURE 2.274. SKULL OF A FOSSIL LEMUR.

FIGURE 2.275. THE SLENDER LORI.

FIGURE 2.276. THE WHITE-NOSED APE.

FIGURE 2.277. THE DRILL-BABOON.

FIGURES 2.278 TO 2.282. SKELETONS OF MAN AND THE ANTHROPOID APES.

FIGURE 2.283. SKULL OF THE JAVA APE-MAN.

FIGURE 2.284. SECTION OF THE HUMAN SKIN.

FIGURE 2.285. EPIDERMIC CELLS.

FIGURE 2.286. RUDIMENTARY LACHRYMAL GLANDS.

FIGURE 2.287. THE FEMALE BREAST.

FIGURE 2.288. MAMMARY GLAND OF A NEW-BORN INFANT.

FIGURE 2.289. EMBRYO OF A BEAR.

FIGURE 2.290. HUMAN EMBRYO.

FIGURE 2.291. CENTRAL MARROW OF A HUMAN EMBRYO.

FIGURES 2.292 AND 2.293. THE HUMAN BRAIN.

FIGURES 2.294 TO 2.296. CENTRAL MARROW OF HUMAN EMBRYO.

FIGURE 2.297. HEAD OF A CHICK EMBRYO.

FIGURE 2.298. BRAIN OF THREE CRANIOTE EMBRYOS.

FIGURE 2.299. BRAIN OF A SHARK.

FIGURE 2.300. BRAIN AND SPINAL CORD OF A FROG.

FIGURE 2.301. BRAIN OF AN OX-EMBRYO.

FIGURES 2.302 AND 2.303. BRAIN OF A HUMAN EMBRYO.

FIGURE 2.304. BRAIN OF THE RABBIT.

FIGURE 2.305. HEAD OF A SHARK.

FIGURES 2.306 TO 2.310. HEADS OF CHICK-EMBRYOS.

FIGURE 2.311. SECTION OF MOUTH OF HUMAN EMBRYO.

FIGURE 2.312. DIAGRAM OF MOUTH-NOSE CAVITY.

FIGURES 2.313 AND 2.314. HEADS OF HUMAN EMBRYOS.

FIGURES 2.315 AND 2.316. FACE OF HUMAN EMBRYO.

FIGURE 2.317. THE HUMAN EYE.

FIGURE 2.318. EYE OF THE CHICK EMBRYO.

FIGURE 2.319. SECTION OF EYE OF A HUMAN EMBRYO.

FIGURE 2.320. THE HUMAN EAR.

FIGURE 2.321. THE BONY LABYRINTH.

FIGURE 2.322. DEVELOPMENT OF THE LABYRINTH.

FIGURE 2.323. PRIMITIVE SKULL OF HUMAN EMBRYO.

FIGURE 2.324. RUDIMENTARY MUSCLES OF THE EAR.

FIGURES 2.325 AND 2.326. THE HUMAN SKELETON.

FIGURE 2.327. THE HUMAN VERTEBRAL COLUMN.

FIGURE 2.328. PIECE OF THE DORSAL CORD.

FIGURES 2.329 AND 2.330. DORSAL VERTEBRAE.

FIGURE 2.331. INTERVERTEBRAL DISK.

FIGURE 2.332. HUMAN SKULL.

FIGURE 2.333. SKULL OF NEW-BORN CHILD.

FIGURE 2.334. HEAD-SKELETON OF A PRIMITIVE FISH.

FIGURE 2.335. SKULLS OF NINE PRIMATES.

FIGURES 2.336 TO 2.338. EVOLUTION OF THE FIN.

FIGURE 2.339. SKELETON OF THE FORE-LEG OF AN AMPHIBIAN.

FIGURE 2.340. SKELETON OF GORILLA'S HAND.

FIGURE 2.341. SKELETON OF HUMAN HAND.

FIGURE 2.342. SKELETON OF HAND OF SIX MAMMALS.

FIGURES 2.343 TO 2.345. ARM AND HAND OF THREE ANTHROPOIDS.

FIGURE 2.346. SECTION OF FISH'S TAIL.

FIGURE 2.347. HUMAN SKELETON.

FIGURE 2.348. SKELETON OF THE GIANT GORILLA.

FIGURE 2.349. THE HUMAN STOMACH.

FIGURE 2.350. SECTION OF THE HEAD OF A RABBIT-EMBRYO.

FIGURE 2.351. SHARK'S TEETH.

FIGURE 2.352. GUT OF A HUMAN EMBRYO.

FIGURES 2.353 AND 2.354. GUT OF A DOG EMBRYO.

FIGURES 2.355 AND 2.356. SECTIONS OF HEAD OF LAMPREY.

FIGURE 2.357. VISCERA OF A HUMAN EMBRYO.

FIGURE 2.358. RED BLOOD-CELLS.

FIGURE 2.359. VASCULAR TISSUE.

FIGURE 2.360. SECTION OF TRUNK OF A CHICK-EMBRYO.

FIGURE 2.361. MEROCYTES.

FIGURE 2.362. VASCULAR SYSTEM OF AN ANNELID.

FIGURE 2.363. HEAD OF A FISH-EMBRYO.

FIGURES 2.364 TO 2.370. THE FIVE ARTERIAL ARCHES.

FIGURES 2.371 AND 2.372. HEART OF A RABBIT-EMBRYO.

FIGURES 2.373 AND 2.374. HEART OF A DOG-EMBRYO.

FIGURES 2.375 TO 2.377. HEART OF A HUMAN EMBRYO.

FIGURE 2.378. HEART OF ADULT MAN.

FIGURE 2.379. SECTION OF HEAD OF A CHICK-EMBRYO.

FIGURE 2.380. SECTION OF A HUMAN EMBRYO.

FIGURES 2.381 AND 2.382. SECTIONS OF A CHICK-EMBRYO.

FIGURE 2.383. EMBRYOS OF SAGITTA.

FIGURE 2.384. KIDNEYS OF BDELLOSTOMA.

FIGURE 2.385. SECTION OF EMBRYONIC SHIELD.

FIGURES 2.386 AND 2.387. PRIMITIVE KIDNEYS.

FIGURE 2.388. PIG-EMBRYO.

FIGURE 2.389. HUMAN EMBRYO.

FIGURES 2.390 TO 2.392. RUDIMENTARY KIDNEYS AND SEXUAL ORGANS.

FIGURES 2.393 AND 2.394. URINARY AND SEXUAL ORGANS OF SALAMANDER.

FIGURE 2.395. PRIMITIVE KIDNEYS OF HUMAN EMBRYO.

FIGURES 2.396 TO 2.398. URINARY ORGANS OF OX-EMBRYOS.

FIGURE 2.399. SEXUAL ORGANS OF WATER-MOLE.

FIGURES 2.400 AND 2.401. ORIGINAL POSITION OF SEXUAL GLANDS.

FIGURE 2.402. UROGENITAL SYSTEM OF HUMAN EMBRYO.

FIGURE 2.403. SECTION OF OVARY.

FIGURES 2.404 TO 2.406. GRAAFIAN FOLLICLES.

FIGURE 2.407. A RIPE GRAAFIAN FOLLICLE.

FIGURE 2.408. THE HUMAN OVUM.

Chapter 2.16. Structure of the Lancelet and the Sea-Squirt.

In turning from the embryology to the phylogeny of man--from the development of the individual to that of the species--we must bear in mind the direct causal connection that exists between these two main branches of the science of human evolution. This important causal nexus finds its simplest expression in "the fundamental law of organic development," the content and purport of which we have fully considered in the first chapter. According to this biogenetic law, ontogeny is a brief and condensed recapitulation of phylogeny. If this compendious reproduction were complete in all cases, it would be very easy to construct the whole story of evolution on an embryonic basis. When we wanted to know the ancestors of any higher organism, and, therefore, of man--to know from what forms the race as a whole has been evolved we should merely have to follow the series of forms in the development of the individual from the ovum; we could then regard each of the successive forms as the representative of an extinct ancestral form. However, this direct application of ontogenetic facts to phylogenetic ideas is possible, without limitations, only in a very small section of the animal kingdom. There are, it is true, still a number of lower invertebrates (for instance, some of the Zoophyta and Vermalia) in which we are justified in recognising at once each embryonic form as the historical reproduction, or silhouette, as it were, of an extinct ancestor. But in the great majority of the animals, and in the case of man, this is impossible, because the embryonic forms themselves have been modified through the change of the conditions of existence, and have lost their original character to some extent. During the immeasurable course of organic history, the many millions of years during which life was developing on our planet, secondary changes of the embryonic forms have taken place in most animals. The young of animals (not only detached larvae, but also the embryos enclosed in the womb) may be modified by the influence of the environment, just as well as the mature organisms are by adaptation to the conditions of life; even species are altered during the embryonic development. Moreover, it is an advantage for all higher organisms (and the advantage is greater the more advanced they are) to curtail and simplify the original course of development, and thus to obliterate the traces of their ancestors. The higher the individual organism is in the animal kingdom, the less completely does it reproduce in its embryonic development the series of its ancestors, for reasons that are as yet only partly known to us. The fact is easily proved by comparing the different developments of higher and lower animals in any single stem.

In order to appreciate this important feature, we have distributed the embryological phenomena in two groups, palingenetic and cenogenetic. Under palingenesis we count those facts of embryology that we can directly regard as a faithful synopsis of the corresponding stem-history. By cenogenesis we understand those embryonic processes which we cannot directly correlate with corresponding evolutionary processes, but must regard as modifications or falsifications of them. With this careful discrimination between palingenetic and cenogenetic phenomena, our biogenetic law assumes the following more precise shape:--The rapid and brief development of the individual (ontogeny) is a condensed synopsis of the long and slow history of the stem (phylogeny): this synopsis is the more faithful and complete in proportion as the original features have been preserved by heredity, and modifications have not been introduced by adaptation.

In order to distinguish correctly between palingenetic and cenogenetic phenomena in embryology, and deduce sound conclusions in connection with stem-history, we must especially make a comparative study of the former. In doing this it is best to employ the methods that have long been used by geologists for the purpose of establishing the succession of the sedimentary rocks in the crust of the earth. This solid crust, which encloses the glowing central mass like a thin shell, is composed of different kinds of rocks: there are, firstly, the volcanic rocks which were formed directly by the cooling at the surface of the molten mass of the earth; secondly, there are the sedimentary rocks, that have been made out of the former by the action of water, and have been laid in successive strata at the bottom of the sea. Each of these sedimentary strata was at first a soft layer of mud; but in the course of thousands of years it condensed into a solid, hard mass of stone (sandstone, limestone, marl, etc.), and at the same time permanently preserved the solid and imperishable bodies that had chanced to fall into the soft mud. Among these bodies, which were either fossilised or left characteristic impressions of their forms in the soft slime, we have especially the more solid parts of the animals and plants that lived and died during the deposit of the slimy strata.

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