328 ANIMAL DEVELOPMENT 



splits the animal into two. Or the groove may be transverse, 

 so that the upper and lower halves of the body are converted 

 into separate individuals. In other cases the attached base of 

 the Anemone grows out into little projections, which are pinched 

 off, and grow into adults. This "laceration", as it has been 

 called, is as much budding as fission. 



Among Corals and allied forms some species are solitary, and 

 these " cup Corals " chiefly differ from Anemones in the possession 

 of a firm calcareous skeleton by which their basal half is sup- 

 ported. Such forms may propagate by budding or fission. But 

 very many kinds of Coral are colonial, and, as in Hydroid Zoo- 

 phytes, each colony has arisen by vegetative propagation of a 

 primary individual. Budding and fission are both exemplified, 

 and there is great variety in the shape of the colonies thus pro- 

 duced. Flat, massive, and branching forms abound in coral-reefs, 

 and may be seen in any museum. 



The regenerative powers of such creatures as Hydroid Zoo- 

 phytes and Sea-Flowers are very considerable, so that " accidental 

 death " is scarcely to be reckoned as one of the dangers to which 

 they are exposed in the course of their existence. The best- 

 known example is afforded by the Freshwater Polype {Hydra), 

 a creature which can be artificially propagated by the simple 

 device of cutting it into pieces. 



Vegetative Propagation and Regeneration in H edge hog- skinned 

 Animals (^Eckinodermata). — The regenerative powers of members 

 of this group are very considerable. Some of the Sea-Cucumbers 

 when seized eject their digestive organs, which are afterwards 

 re -developed. Sea- Lilies and Feather- Stars can also survive 

 the loss of their soft parts, quickly replacing them by a new set. 

 Star-Fishes and Brittle-Stars are quite notorious for the rapidity 

 with which they renew lost arms. This is the origin of " comet " 

 forms, in which some of the arms are of small size, being, in fact, 

 new members which have yet to reach their full size. 



Fission is definitely known to take place in some of the 

 Star- Fishes and Brittle-Stars, the body being divided into two 

 approximately equal parts. But the most remarkable illustration 

 of vegetative propagation is met with in one family [Linckiidce) 

 of the former group. In Star- Fishes of this kind one or more 

 arms can be deliberately thrown off Not only is the original 

 individual able to grow these again, but each detached arm can 



