jANU.MY^e, 1906.] 



SCIENCE. 



149 



physical conditions. We have based this dis- 

 cussion upon North American types because 

 the physical aspect of the barriers are not so 

 pronounced as in some other parts of the 

 world and because we wished to emphasize the 

 psychological aspect of these barriers. Al- 

 though the writer knows nothing of the bio- 

 logical problem that has been discussed in 

 these pages, he ventures to suggest that the 

 habits of animals formed in response to en- 

 vironmental conditions may become psycholog- 

 ical barriers to diffusion. There may be a 

 kind of psychophysical at-home feeling that 

 ties a species to certain areas. 



Clark ' Wissler. 



SPECIAL AUrWLEH. 

 PHYSIOLOGICAL REGENERATION IN INSECTS. 



Morgan in ' Eegeneration ' (1901), p. 19, 

 defines physiological regeneration as follows: 



Finally, there are certain normal changes that 

 occur in animals and plants that are not the 

 result of injury to the organism, and these have 

 many points in common with the processes of re- 

 generation. They are generally spoken of as 

 processes of physiological regeneration. The an- 

 nual moulting of the feathers of birds, the periodic 

 loss and growth of the horns of stags, the break- 

 ing down of cells in the different parts of the 

 body after they have been active for a time, and 

 their replacement by new cells, the loss of the 

 peristome in the protozoon, Stentor, and its re- 

 newal by a new peristome, are examples of physio- 

 logical regeneration. This group of phenomena 

 must also be included under the term ' regenera- 

 tion ' since it is not so sharply separated from that 

 including those cases of regeneration after injury, 

 or loss of a part, and both processes appear to 

 involve the same factors. 



Again, on p. 25 (ibid.), Morgan says that 

 he will use the term physiological regeneration 

 to include such changes " as the moulting and 

 replacement of the feathers of birds, the re- 

 placement of teeth, etc. — changes that are a 

 part of the life-cycle of the individual. In 

 some cases it can be shown that these processes 

 are clearly related to ordinary regeneration, 

 as when a feather pulled out is formed anew 

 without waiting for the next moulting period, 

 and formed presumably out of the same rudi- 



ment that would have made the new feather in 

 the ordinary moulting process." 



Finally, on pp. 128-131 {ibid.), Morgan 

 refers to the general fact that ' in the same 

 animal certain organs may be continually 

 worn away and as slowly replaced, and other 

 organs replaced only at regular intervals,' 

 and he lists a number of familiar instances 

 of regularly recurring physiological regenera- 

 tion, as the moulting of snakes, the throwing 

 off of deer antlers and their renewing, and 

 also the moulting of insects. As this is the 

 only instance of physiological regeneration in 

 insects mentioned by the author, and as it 

 seems to be desirable to know, especially as a 

 basis for any discussion of the relation be- 

 tween ' physiological regeneration ' and the 

 more familiar restorative phenomenon called 

 simply ' regeneration,' of any other instances 

 of physiological regeneration occurring among 

 the lower animals — almost all the cited cases 

 of physiological regeneration are among the 

 vertebrates — I wish to point out briefly cer- 

 tain important and widespread phenomena in 

 insect biology which should be included in the 

 category of physiological regeneration proc- 

 esses. Indeed, Morgan specifically ' refers to 

 the need of such further knowledge. " How 

 far," he says, " physiologital regeneration 

 takes place in the tissues of the lower animals 

 we do not know at present except in a few 

 cases, but far from supposing it to be absent, 

 it may be as well developed as in higher 

 forms." 



First may be mentioned the radical regen- 

 eration of the digestive epithelium of the 

 ventriculus, common to all ( ?) insects, a 

 phenomenon long known, albeit in a rather 

 hazy way perhaps, to students of insect mor- 

 phology, but in the last ten years carefully 

 studied and satisfactorily worked out for a 

 number of insect forms representing several 

 widely separated orders. (See the papers of 

 Mobusz, Eengel, Van Gehuchten, ISTeedham 

 and others.) This process consists of. the con- 

 stant senescence and complete degeneration of 

 the nuclei and cytoplasm of the large epithelial 

 cells of the ventricular portion of the alimen- 

 tary canal and of the equally constant appear- 

 ance of new nuclei in conspicuous small 



