324 Dr. C. F. Liitken on Spontaneous 



at ray command gives the impression that if the act is not re- 

 newed it generally occurs at an early age, and that the lost 

 parts sprout forth as the general growth goes on. Hence the 

 larger the specimens the nearer they approach the normal 

 state (six equal arms, &c), and the smaller they are (down to 

 a certain limit) the more they approach the divided form with 

 three arms. This rule, however, is by no means without ex- 

 ceptions. Sometimes also the division takes place unequally, 

 so that we meet with specimens with four large and two small 

 arms, or with four small and two large arms ; but these cases 

 are rare. 



In the case before us the phenomenon would certainly seem 

 to be capable of another interpretation — namely, that these 

 Ophiurids quit the larval state as half individuals, that is to 

 say with three arms (exceptionally four or two) and half (one- 

 third or two-thirds) of the disk, and that the parts deficient are 

 gradually developed ; but this interpretation would be imme- 

 diately rejected as absurd. They might rather, originally, 

 have the whole disk and three arms, so that the new arms 

 might grow in the intervals between the old ones ; but although 

 we sometimes meet with six-armed starfishes (Linckia) with 

 three short arms and three longer ones alternating with the 

 former, which would seem to support this hypothesis, this mode 

 of development has not been observed in any Asterid or 

 Ophiurid*. 



There is yet another question — namely, whether this division 

 is entirely voluntary (*". e. a natural spontaneous division) or 

 involunfary («. e. the consequence of exterior violence, of a 

 special lesion so frequent that very few individuals can escape 

 it). The faculty of regeneration is certainly gTeat among the 

 Ophiurids. The disk of an Ophiura deprived of all its arms 

 might undoubtedly, under favourable circumstances, regenerate 

 them all ; and it is probable that an injury which at the same 

 time removed a small portion of the disk, would be reparable 

 in the same way; at least, I have met with Ophiurids, e.g. 

 Opliiodermavirescens ,the disk of which bore indisputable traces 

 of a partial regeneration of this kind after an accidental in- 

 jury ; and I should not be surprised if experiments of arti- 

 ficial division were successful in many cases, especially with 

 young Ophiurids. It would not, however, be right to con- 

 clude from this that the phenomenon described in Ophiothela 



* In connexion with this, Opkiacantha anomala and O. vivipara are of 

 interest as Ophiurids with more than five arms (six to eight) which 

 originate with all their arms. It is only in some Asterids, in which the 

 number of arms is very great, that new arms continue during growth to 

 sprout forth between the old ones. To this we shall recur hereafter. 



