REPRODUCTION AND HEREDITY 253 



grisea that all body-cells became completely severed, lived inde- 

 pendently for several months, and crawled about like amoebae. 

 Jager suspected that the individual cells hibernate in this state 

 and develop into complete polypes in the following spring. 



In the other relatives of Hydra, the sea-anemones and corals, 

 this regenerative faculty is still equally well developed. In 

 numerous species of higher multicellular organisms, most of the 

 worms, echinoderms and tunicates, the power of regeneration is 

 frequently very strong. One may often observe, for instance, how 

 an earth-worm, attacked by a myriapod, separates in the middle, 

 thus saving its life by sacrificing part of its body. The anterior 

 end is in that case able to reproduce a new posterior end, while 

 the latter can reproduce a new anterior part. 



The enormous tenacity of many Turbellarians is astounding. 

 For example, we may cut up a Planarian into longitudinal and 

 transverse sections and yet see how each part once more develops 

 under favourable conditions into a complete organism. In this 

 almost indestructible creature one may easily reproduce the 

 strangest malformations, for the slightest injuries are sufficient 

 to stimulate the body-cells into regeneration. If, for instance, 

 we make several incisions into the body of a Planarian new 

 anterior or posterior parts will be formed in these spots, according 

 to the direction of the incision. 



We heard on a previous occasion that the starfishes are able, 

 by constriction, to shed their arms, and that each arm is able to 

 re-grow a complete star. The sea-cucumbers are able at touch, 

 or after prolonged captivity, to eject, by means of powerful con- 

 traction of all the muscles of the body, their intestines through 

 mouth and anus, without suffering any vital injuries from this 

 horrible mutilation. In the molluscs and arthropods the re- 

 generative faculty has considerably decreased, being restricted 

 to the re-growing of tentacles and syphons, or to the supplement- 

 ing of lost legs, antennae, or claws. In a few rare cases more 

 important organs may be repaired : for instance, eyes in crabs. I 

 must not omit here to point out a remarkable experiment made 

 by Herbst. If he removed the eye of one of the higher crusta- 

 ceans, together with the eye ganglion, an antenna was developed 

 in place of an eye ; if, however, only an eye was removed and 

 the nerve-centre left intact regeneration of an eye took place 

 with perfect regularity. 



