424 THE METHOD OF ORGANIC EVOLUTION. 



cervical or neck vertebriii of mammalia to seven joints. This number 

 is wonderfully constant, being the same in the long necks of the giraffe 

 and camel and the very short necks of the hippopotamus, porpoise, and 

 7nolc, the only exceptions in the whole class being some of the sloths, 

 which have from six to ten, often varying in the same species, and the 

 manatee, which has six. 



Now, if M^e consider the enormous extent of these fixed numerical 

 relations of important parts of the organism in the higher vertebrates 

 and in insects, both as regards the number of living species affected — 

 perha])s 99 i)er cent of the whole — and as regards their range in time, 

 throughout the whole of the Tertiary and Secondary, ami even a con- 

 siderable portion of the Paleozoic periods, and if we take account of the 

 vast number of extinct species, genera, and families needful to com- 

 plete the various lines of descent from the earliest known forms, pre- 

 senting the same numerical relations to those now living, we shall be 

 able to form .some conception, however inadequate, of the overwhelming 

 frequency and importance of variations in the size, form, proportions, 

 and structure of the various- parts and organs of the higher animals, 

 as compared with variations in their number. No doubt in the earlier 

 stages of organic development numerical variations were more frequent 

 and more important, as they are now among the lower forms of life; but 

 at a very early period in geological history the main numerical relations 

 of the essential parts of the higher organisms became more or less fixed 

 and stable, and have in many cases remained unchanged through a 

 large proportion of the i)eriod comi^rised in the geological record. The 

 four limbs of vertebrates were already established in the fishes of the 

 Devonian period, as were the four wings and six legs of true insects in 

 the cockroaches and archaic orthoptera of the Carboniferous; and 

 almost all subseqiTcnt changes have resulted from modifications of these 

 early types. The earliest mammals of which we have sufficient knowl- 

 edge have the typical five-toed feet, and the earliest l)irds appear to 

 have had the same progressive series of toe joints as now prevails. 



We are thus irresistibly led to the conclusion that, among all the 

 possible forms of variation now occurring, those affecting the number 

 of imi)ortaiit serial ])arts among higher organisms are those which 

 have the least possible relation to whatever modification of species 

 may now be going on around us, or which has been going on dur- 

 ing a large jiortion of geological time. Yet it is to variations of this 

 nature, a large ])ioportion of which are mere malformations or mon- 

 strosities, that the bulky and learned volume we are discussing has 

 been devoted. The author of this book puts forward these malfor- 

 mations and irregularities, mixed up with a proportion of normal 

 variations, under the misleading name of '^Discontinuous variations," 

 as if they were something new, and had been ignorantly overlooked 

 by Darwin and his followers; and he loses no opportunity of telling 

 us how important he thinks they are, what difficulties they enable us 



