The Recapitulation Theory in Biology 41 



a number of branches which pass between the pharyngeal aper- 

 tures — which permanently characterize these organs in fishes. 

 The skeleton, largely bony in the adult, passes through a stage 

 in which it is entirely without bone, and consists mainly of carti- 

 lage — the form which it permanently possesses in certain fishes. 

 Further, the vertebrate embryo possesses for a time a notocord, a 

 segmented muscular system, a continuity between the pericar- 

 dium and the posterior part of the perivisceral cavity — all 

 features which characterize certain groups of Pisces in the adult 

 state. Instances of this kind might be multiplied for the work 

 of anatomists and embryologists has of late years been largely 

 devoted to adding to them." 86 



There is no disposition evident on the part of biological stu- 

 dents to deny the ancestral reference of this class of facts. Opin- 

 ion differs as to the sense in which they are to be regarded as 

 ancestral. These differences of opinion are reported in the 

 second section following. But it is important to note that 

 such facts coexist with other embryonic conditions for which 

 no ancestral reference is found. For instance, 



"Examples of embryonic characters which are not found in 

 the adults of other vertebrates are the following: At a certain 

 stage of development the central nervous system has the form 

 of a groove in the skin, there is a communication at the hind 

 end of the body between the neural and alimentary canals, the 

 mouth aperture at the first has the form of an elongated slit, 

 the growing end of the Wolffian duct is in some groups continuous 

 with the ectoderm, and the retina is at one stage a portion of 

 the wall of the medullary canal. In the embryos of the lower 

 Vertebrates many other instances of the same interesting char- 

 acter might be mentioned." 66 



IS. Recapitulation and the Physiology of Development. 



The later history of recapitulation has been seriously affected 

 by two lines of thought which combined to unsettle some of 

 its primary assumptions. These followed upon the gradual 



"Encyclopaedia Britannlca, 11th edition, art. Embryology, p. 322. 



<• IUd., 



For a statement of the evidence favorable to recapitulation, see Marshall, Lectures 

 on the Darwinian Theory. 1894, and Biological Lectures and Addresses, 1894, by the same 

 author. Miall's comment on the presentation of Marshall is, "Development tells 

 us something, I admit, and that something Is welcome, but it gives no answer at all 

 to most of the questions we put. . . . The best facts of the Recapitulationist 

 are striking and valuable, but they are much rarer than the thoroughgoing Recapitu- 

 lationist admits; he has picked out all the big strawberries and put them at the top 

 of the basket." Brit. Assoc, for the Adv. of Science, 1897, p. 682. 



