PRESENT PKOBLEMS I\ EVOLUTION AND lIEKEDrrV. 349 



Among' the lowoi- animals we lind tlic samt' power: ilwccnt a liydia 

 or bell animal('ul(! into a dozen pieces, eaeli may re]>i()iln('e a perfect 

 new indivichuil. As we ascend in the animal scale the ] tower is coii- 

 lined to the rei)roduction of a lost i>art in the proce8s known as recres- 

 cence. As you well know, in the group to which the frog and sala- 

 mander belong, a linil) or tail, or e\ en a lower jaw, may berei)rodnced. 

 The only logical inter})retation of these ]»henomenii is that the heredi- 

 tary powers are distributed in the entire protoplasm of the organism, 

 and the capacity of icproduction is not exlniusted in the original for- 

 mation of the limb, but is capable of being repeated. There has been 

 considerable discussion of late as to the seat of this power of recrescen<'e. 

 It seems to me not impossibh' that in the vertebrates it may be stored 

 in the germ cells, and it would be very interesting to ascertain experi- 

 mentally whether removal of these cells would in any way limit or 

 affect this power: we know that such removal in castration or ovari- 

 otomy sometimes piofoundly modifies the entire nature of the organ- 

 ism, causing nuile characters to appear in the female, and female char- 

 acters to develo]> in the male. 



So far as man is concerned it has been claimed by surgeons that 

 genuine recrescence sometimes occurs ; for example, that anew head is 

 formed upon the femur after exsection ; but my friend Dr. Y. P. Gibney 

 informs me that this is an exaggeration, that there is no tendency to 

 repioduce a true head, but that a pseudo-head is formed, which may 

 be explained upon the ijriuciple of regeneration and individual tians- 

 formism by use of the limb. 



Ptliiger's opinicm is that recrescence does not indicate a storage of 

 hereditary power, that there is no pre-existing germ ol' the mend)er, 

 but that the re-growth is due to the organizing and distributing power 

 of the cells at the exjtoscd surface, so that, as new formative nuitter 

 arrives, it is bnilt np gradually into the limb. This view would reduce 

 recrescence to the level of the regeneration process which nnites two 

 cut sections of the elements of a limb in their fornu'r order. It is jtartly 

 opposed to the faints above referred to, which seem to prove th<' dis- 

 tiibutiou of the hereditary i)ower. Y'et it seems to me (piite consistent 

 toc(»iisider these tlirec processes— a, I'eproduction of a new individnal 

 from every ])art; It, recrescence of a new mend)er horn any part; r, w- 

 geiieration of lost tissues — as three steps indicating the gi-adnal, but 

 not entire withdrawal of the reproductive power into the germ cells. 



1 have not space to cDiisider all the gronnds whicli support the view 

 of the separation of the g<'rm cells in man. Some of the more i)romi- 

 nent are: the very early ditferentiation of these cells in the embry<), 

 obscrxcd with a few exc('[)ti()ns in all the h)wer orders of animals, and 

 advancing si» rapidly in the human female that several months before 

 l)irth the number of primordial ova is estimated at seventy thousand, 

 and is not believed to be increased after the age of two and a half 

 years. The most patent practical proof is that we may remove every 



