LINXEAN SOCIETY OF LONDON. 6 1 



might be called the " persistence theory " of recapitulation, and 

 against the theory of accelerated adult incorporations. A tiny 

 Btalked larva was probably a feature of every Crinoid from 

 Cambrian age to the present ; the heterocercal tail of a Teleost 

 larva was found in the larval as well as in the adult stage of a 

 Sturgeon ; ti.e " Emar;/ inula'' stage of Fissurdia was much closer 

 to the early post-larval stage of Emanjinula than to its final con- 

 dition ; the larval Portnnion lacked the last thoracic feet, like every 

 other Isopod larva; and a Tadpole resembled the larva of a 

 Pohjpferus or Dipnoan far more closely than it resembled the 

 adult of any possible Piscine or Stegocephalic ancestor. 



The so-called law of " tachygenesis ''' had been made much of by 

 palaeontologists. But in the case of Ammonites we had no means 

 of distinguisliing between environmental influences and hereditary 

 factors. The Echinospira larvte of Lamellaria showed how deeply 

 environmental influences might affect the growth of jjclagic shells, 

 so as to produce a cyclical series of changes as complete as in any 

 Ammonite, yet independent of any influence from successive adult 

 ancestors. 



The discussion was continued by Prof. E. W. MacBride, F.R.S. 

 (visitor). Dr. F. A. Bather, F.ll.S. (visitor). Prof. E. S. Goodrich, 

 F.R..S., See.L.S., Dr. D. H. Scott, F.R.S., Dr. W.Bateson, F.E.S., 

 Dr. W. D. Lang (visitor), Mrs. C. B. Hodson, and the President, 

 Prof. Garstang replying. 



Prof. E. S. Goodrich agreed witb Prof. Garstang that an 

 organism in its development does not recapitulate its phylogeny, 

 but merely tends to repeat the ontogenetic stages of its immediate 

 ancestor. He pointed out a fundamental fallacy in the argument 

 for Recapitulation when it assumes that organisms start their 

 development from the same point as their ancestors. Taking for 

 instance the Fish, Amphibian, Reptile, and Mammal, as stages in 

 phylogeny, the Amphibian does not start as a Fish, travelling 

 along the same road and proceeding a liltle farl-her. Still less 

 does the Mammal start as a Fish or Amphibian or even a Reptile; 

 its egg is mammalian from the first. The successive stages differ 

 essentially as much from each other in the egg as they do in the 

 adult. In so far as they tend to pass through the same develop- 

 mental stages as their near ancestor, it is because they start with 

 approximately the same complex of transmitted factors of 

 inheritance and develop under the same conditions. Phenacodus, 

 Hijracotlierium, Mesoliippus may be considered to represent stages 

 in the phylogeny of the horse. But we may infer that if the 

 one-toed Horse passes through a three-toed stage, it is because its 

 near ancestor the three-toed MesoluppuslmiX an embryo with three 

 w-ell-dnveloped toes ; and so on down the series. Such cases may 

 be compared to the alleged instances of recai)ituh>tion among 

 Ammonites and other fossil Invertebrates. The case of the 

 Brazilian tortoise, cited bv Prof. MacBride, differs in no essential 

 from that of Portunion. The tortoise passes through a "chelonian" 

 hard-shelled stage before it becomes soft and adapted to life in 



