chap, xiii.] REPRODUCTION OF ECHINODERMS. 493 



it would appear that the arms often break off for the 

 purpose of more effectually evacuating their genital 

 products. In some cases, ordinary five-rayed forms, 

 such as the common starfish, have been seen to, 

 as it were spontaneously, break off an arm ; from 

 such a single arm several new rays are budded off, and 

 as these only gradually grow, such a starfish has the 

 appearance of a comet, or body with a long tail. In 

 the case of the Ophiuroids, it is, owing to the cen- 

 tralisation of the organs, necessary that this mode of 

 multiplication should be effected not by the separa- 

 tion of a single arm, but by the division of the disc, 

 and Ophiuroids are not ^infrequently to be seen in 

 which there are three shorter, and two or three longer 

 arms, the members of either set being subequal among 

 themselves. The reproduction of arms is also to 

 be frequently noticed among the Crinoids, but we 

 have not yet sufficient information as to whether these 

 arms have been directly broken off by enemies, or 

 set free by their possessor in consequence of an in- 

 herited peculiarity, as observed by Jickeli in Antedon 

 rosacea, or from fear of danger. This kind of repro- 

 duction has not been observed, as may well be sup- 

 posed, among Echinoids, but it is well known that 

 Holothurians will, if terrified, eject their viscera, and 

 gradually redevelop what one must suppose to be im- 

 portant organs ; the Crinoids will replace the whole 

 of the viscera contained in their calyx (M. Marshall). 



The various stages of reproduction and fusion 

 which are to be observed among Echinoderms can be 

 nearly all paralleled by what is to be seen in dif- 

 ferent groups of the animal kingdom. An annelid of 

 the southern seas (Palolo) is said to evacuate its 

 genital products by completely breaking into pieces, 

 when the ova and spermatozoa meet and unite in the 

 water ; the loss of a single arm may be compared to 

 the gradual break-up of the organism which is seen in 



