76 



SCIENCE 



[N. S. Vol. LI. No. 1308 



for, from it lie derives the support of his 

 orthogenesis. Since the same kinds of ad- 

 vances are observed over and over again in 

 different groups, and since no plausible reason 

 can be given why such changes are of benefit 

 to the species, it follows, on Whitman's view, 

 that some internal agency has brought about 

 these parallel advances. 



The change at molting that transforms the 

 young plumage into that of the adult is often 

 abrupt, almost like a mutation, yet a simple 

 ejqDeriment shows that in the interval the con- 

 stitution of the bird has been progressively 

 advancing. If feathers are plucked in the 

 intervening stages, the new feathers show an 

 advance over the young feathers still present, 

 an advance in the direction of the feathers 

 that are to come at the next molt. And the 

 nearer to molting time the operation is per- 

 formed the nearer the approach to the newer 

 feathers. Here then what appears to be a 

 sudden change has in reality been led up to 

 by a continuous series of preparatory stages; 

 so, in Whitman's view, what appear at times 

 to be sudden and great changes in evolution 

 (mutations) are in reality only end stages of 

 continuous advance. The development of the 

 bird repeating the history of the race shows 

 continuous change but the exegesis of molt- 

 ing gives us only the earlier and the later 

 picture. To discuss this theme would take us 

 too far afield, but it is a matter not unfamiliar 

 to the morphologist. It should be pointed out 

 that a change (mutation) in the germ-plasm 

 affecting principally the end stages would be 

 expected to give residts that are in no sense 

 incompatible with this picture. 



Whitman obtained a few "mutations," i. e., 

 new types of pattern that were transmitted. 

 The mutant change, he points out, is only an 

 extension of a character already faintly pres- 

 ent in the birds and present in certain wild 

 species. What is produced is not new but a 

 " continuous " extension of a character al- 

 ready present. Hence such mutations are not, 

 he contends, new unit-characters but exten- 

 sion or diminution of characters already in 

 existence. Such, in fact, are the majority of 

 mutations known to us to-day. 



Whitman thinks a very old idea reincar- 

 nated in Darwin's theory of pangenesis (that 

 the body characters impress their influence on 

 the germ cells) while nominally rejected sur- 

 vives in more subtle guise in some more 

 modem theories such as de Vries's theory of 

 pangenesis. In this theory the nucleus is 

 looked upon as the seat of the hereditary com- 

 plex. Its " vital " units are self -perpetuating 

 by division, so that the nucletis in every cell 

 remains the store house of all of the hereditary 

 materials. In the course of embryonic de- 

 velopment these vital elements, pangenes or 

 genes, are set free in the surrounding cyto- 

 plasm of the cell, where they multiply and 

 determine the fate of the cell. " The mjth of 

 transmission was not eliminated; it was only 

 reduced in its field." " Transmission thus be- 

 came more direct, but its mysteries remained 

 as imfathomable as before. The imit-char- 

 acters are assumed to preexist in the chromo- 

 somes and to stand in need of transportation 

 from the nucleus to the body of the cell in 

 order to develop." But " if an innumerable 

 host of specifically distinct unit-characters are 

 let loose in the cell-plasm, how are they to 

 reach precisely predetermined points in the 

 organism, and at just the time when needed? 

 It is here that the theory breaks down, for 

 the difficulty is not one that further investi- 

 gation may hope to solve, but one that lands 

 us in hopeless speculation. So long as the 

 primary assumption is that of ready-made 

 unit-characters, specifically distinct and inde- 

 pendently variable, whether located in the 

 nucleus or in the cytoplasm, or in both, the 

 problem of development will remain in- 

 scrutable." 



A perusal of de Yries's pangenesis theory 

 will show that Whitman has put his finger on 

 a weak spot in the specidation, in so far as 

 this view pretends to explain how the specific 

 pangens of the nucleus are supposed to 

 migrate out of the nucleus of each cell at the 

 right time in particular regions of the em- 

 bryo, but de Vries laid no emphasis on this 

 and was familiar with the absence of evidence 

 for such an interpretation. The same diffi- 

 culty confronts us to-day, but if I understand 



