680 REPORT— 1901. 



in a remote way suggested a member of the zebra family. All my hybrids, like 

 those bred in Brazil, have more stripes than their zebra sire, and in some of them 

 the bands are nearly as conspicuous as in some of the zebras, thus proving that 

 both the mares (which varied in colour and breed) and the two zebra stallions 

 used were well adapted for the experiment. The results of my experiments, not 

 only with the Equidre but also with other domestic quadrupeds and birds, all point 

 to the conclusion that there is no such thing as telegony, and the same conclusion 

 has been independently arrived at by Baron de Parana in Brazil. Believers in 

 telegony — tliey are numeroua in America, India, and Australasia, as well as in 

 England — almost always say of the many experiments recently made with a view 

 to giving ' infection ' a chance of showing itself, that they have only yielded 

 negative results, and they generally add, it is impossible to prove a negative. After 

 carefully considering all the more striking so-called cases of 'infection,' I have no 

 hesitation in saying that there is no satisfactory evidence that there has ever been, 

 either in the human family or amongst domestic animals, a single instance of 

 ' infection.' 



I have in a hurried and imperfect manner indicated that we are not likely to 

 find either in maternal impressions, the direct action of the environment, use- 

 inheritance, or telegony a true cause of variation. I have endeavoured to point 

 out that, instead of simply stating that variation is due to the constant recurrence 

 of slight inequalities of nutrition of the germ-cells, we may with some confidence 

 assert that diliereuces in the age, vigour, and health of the parents and diSerencea 

 in the ripeness of the germ-cells are potent causes of variation. 



I have also endeavoured to prove that intercrossing, though a direct cause of 

 retrogressive variation, is only an indirect cause of progressive variation, while 

 interbreeding (in-and-in-breeding) at the right moment is a cause of progressive 

 variation. 



Further, I have discussed at some length the swamping effects oc inter- 

 crossing, chiefly with the object of showing (1) that progress in a single direction 

 is probably often due to new varieties swamping old, it may be long-established, 

 varieties ; and (2) tbat several varieties may be sutlicientlv exclusive to flourish 

 side by side in the same area, and eventually (partly owing to their aloofness, i.e., 

 to differential mating) give rise to several new species. 



I have only now to add that I was mainly led to select ' The Experimental 

 Study of Variation ' as the subject of my address that I might indirectly indicate 

 that the time had come when a well equipped institute should be provided for 

 biological and other experiments. 



The following Papers and Reports were read :— 



1. I'he Pelvic Cavity of the Porpoise (Phocoena communis) as a guide to the 

 determination of a, Sacral Region in Cetacea. By David Hepburn, 

 M.D., F.R.S.E., Lecturer on Rpgioncd Anatomy, and David Water- 

 STON, M.A., M.D., F.R.S.B., Demonstrator of AncUomy, University of 

 Edinhiurgh. 



Among Cetacea the absence of hind limbs renders it difficult to determine from 

 external examination where the trunk of the body ends and the tail begins, but 

 upon the skeleton the y)resence of chevrons enables us to differentiate the caudal 

 from the so-called lumbar vertebrre. No means of subdividing the lumbar verte- 

 brae into lumbar and sacral sets having hitherto been suggested, the authors are of 

 opinion that a key to such subdivision may be found in a study of the vertebral 

 relations of the pelvic cavity. They have determined the existence of a true pelvic 

 cavity in the common porpoise. This cavity corresponds to five prae-caudal verte- 

 brre, and its anterior end is opposite the 29th vertebra behind the skull. The 

 authors have examined the vertebral columns of a number of four-footed mammals 

 and find that the first segment of the fused sacrum varies in position from the 

 27th to the 31st vertebra behind the skull. Among Cetacea they find that 



