402 BIOLOGY: GENERAL AND MEDICAL 



moulds itself into the exact form of that which was lost 

 and eventually comes to perform its function. So the 

 phenomena of regeneration include simple healing, the 

 rearrangement of the entire organism, or the restitution 

 of the lost part. 



It is easy to understand that cells are continually 

 multiplying in the rete mucosum, in the nail matrix, or in 

 the hair follicles, undergoing a regular series of trans- 

 formations and ending, respectively, in horny epiderm, 

 nails, and hairs, all of which are relatively simple struc- 

 tures; but when a peacock moults and the regenerative 

 process is called upon to produce large, elaborately deco- 

 rated, and beautifully colored feathers, each of which 

 bears a definite relation of size and figure to the geomet- 

 rically proportioned pattern of the bird's spread tail, 

 one cannot help feeling that something more than 

 local conditions are engaged in the new formation. 



Each year the antlers of the stag are shed, but grow 

 again as soft spongy osseous formations which become 

 more and more dense or eburnized until of ivory hardness. 

 Each year the antler develops along new lines, increas- 

 ing in size and complexity according to the age of the 

 stag, always in conformity with the type of the species, 

 but never twice, the same in the same individual. Here 

 there can be no doubt about the hereditary character 

 of the influences controlling the regeneration. 



When the repair following injury is carefully con- 

 sidered, we again find that it is less simple than at first 

 appears, for the closure of the wound by cicatricial tissue 

 and its covering by a new growth of the ectoderm is 

 complicated by a more or less pronounced tendency 

 toward the renewal of those parts that may have been 

 destroyed or removed. 



The present knowledge of the subject is insufficient 

 to enable the phenomena of regeneration to be reduced 

 to orderly scientific principles; we no doubt confuse 

 different processes with one another. The following 

 arrangement may enable the student to appreciate 



