August 16, 1901.] 



SCIENCE 



243 



more rapidly from the base than at a 

 more distal level. It may appear at first 

 thought, that the more rapid regeneration 

 of the arm at the place at which it is 

 usually thrown off may be associated with 

 its more frequent loss at this region — in 

 other words, that the more rapid regene-; 

 ration has been acquired by the region 

 at which the arm is generally broken off. 

 This interpretation is, however, excluded 

 by the fact that, in general, the nearer to 

 the base the arm is cut off, so much the 

 more rapid is its regeneration. In other 

 words, the more rapid regeneration of the 

 arm at the base is only a part of a general 

 law that holds throughout the arm. If the 

 proposition is reversed, and it is claimed 

 that the arm has acquired the property of 

 breaking off at the base, because it regener- 

 ates more rapidly at that level, the follow- 

 ing fact recorded by King is of importance, 

 viz., that although the arm regenerates 

 faster at the base, yet a new arm is not any 

 sooner produced in this way, since there is 

 more to be produced, and the new arm from 

 the base may never catch up to one grow- 

 ing less rapidly from a more distal cut sur- 

 face, but having a nearer goal to reach. 



The results of our examination show that 

 those forms that are liable to have certain 

 parts of their bodies injured are able to re- 

 generate not only these parts, but at the 

 same time other parts of the body that are 

 not subject to injury. The most remark- 

 able instance of this sort is found in those 

 animals having breaking-joints. We find 

 in these forms that regeneration takes place 

 •both proximal and distal to this region. If 

 the power of regeneration is connected with 

 the liability of a part to injury, this fact is 

 inexplicable. 



If we turn now to the question as to 

 whether regeneration takes place in those 

 species that are subject to injury more 

 frequently or better than in other species, 

 we find that the data are not very complete 



or satisfactory for such an examination. 

 It is not easy to tell to what extent differ- 

 ent animals are exposed to injury. If we 

 pass in review the main groups of the 

 animal kingdom, we can at least gain some 

 interesting facts in this connection. 



In the Protozoa nucleated pieces have 

 been found to regenerate in all forms that 

 have been examined, including amoeba, dif- 

 flugia, thalassicoUa, paramcecium, stentor, 

 and a number of other ciliate infusoria. 



In the sponges it has been found by 

 Oscar Schmidt that pieces may produce 

 new individuals, but how widely this oc- 

 curs in the group is not known. In the 

 ccelenterates many forms are known to re- 

 generate, and it is not improbable that in 

 one way or another the process occurs 

 throughout the group. The hydroid forms, 

 hydra, tubularia, parypha, eudendrium, an- 

 tennularia, hydractinia, podocoryne, etc.; 

 the jelly-fish, gonionemus, and certain mem- 

 bers of the family TJiaumantidce, have been 

 found to regenerate. Amongst the Scyphozoa, 

 the metridium, cerianthus and the scyphis- 

 toma of aurelia regenerate and the jelly- 

 fishes belonging to this group have a limited 

 amount of regenerative power. 



In the Platodes we find all the triclads, 

 that have been examined, including plan- 

 aria, phagocata, dendrocselum, and the land 

 triclad bipalium, regenerate. It has been 

 shown that the marine triclads also regen- 

 erate, but less rapidly and extensively, while 

 the marine polyclads have very limited 

 power of regeneration. The regeneration 

 of the trematodes and cestodes has not, 

 so far as I know, been studied, neither have 

 the nematodes been examined from this 

 point of view. 



Some of the nemerteans regenerate, others 

 do not seem to have this power. A small 

 fresh water form, tetrastemma, that I ex- 

 amined did not regenerate although some 

 of the pieces, that were filled with eggs, re- 

 mained alive for several months. 



