326 Dr. C. F. Liitken on Spontaneous 



tirely deficient, but the wound is already closed and cicatrized ; 

 a larger specimen has in part regenerated its deficiencies, but 

 the new half of the disk and the new arms are much less de- 

 veloped than the others. This is also the case, although in a 

 somewhat different degree, with the two largest of these four 

 specimens (diameter of disk 3'5-4 millims. ; longest arms about 

 20 millims.) ; in one the three new arms are half the length and 

 thickness of the others, and in the other they are only 2 millims. 

 long and of proportionate thickness, the new half of the disk 

 presenting a corresponding development. If we may draw 

 any conclusion from this little series of observations, it would 

 be that the division occurs twice in this species — first, in 

 very small individuals, and then in those which are adult or 

 nearly so. 



All the specimens of OpMactis sexradia, Gr. {0. Rein- 

 hardti, m.), that I have examined have six arms, and in 

 general, especially in the large specimens, there is no striking 

 difference between the arms ; it is only in some of the small 

 ones that one of the groups of arms is in course of regenera- 

 tion. Such is also the case in one of the two small specimens 

 of OpMactismrenSj Sars, from the Mediterranean, which I have 

 had the opportunity of seeing. Sars says of this species that all 

 his 23 specimens had six arms, and that in nearly half of them 

 " the three arms situated on one side were much shorter and 

 thinner than the others, and evidently regenerated after a loss 

 or division." With regard to 0. virescens of the west coast 

 of America, Mr. Verrill* states that he has always found six 

 arms, but that many young individuals had only three, the 

 three on one side being entirely deficient or very small, as if 

 in course of regeneration. Out of 13 specimens I found 12 

 with six arms, partly unequal ; the thirteenth, which is one of 

 the largest, has five equal arms. I have always found 0. 

 Krebsii with six arms : a great number of the small individuals 

 show the regeneration ; the large specimens always have the 

 arms and the radii of the disk equally developed. Of 0. Mi'd- 

 leri most of the smaller examples have six unequal arms ; but 

 there is a certain number with five equal arms ; and most of 

 the adult specimens seem to be in the latter condition. 



Except in the above-mentioned genera I only know of a 

 single instance of heteractinism among the Ophiurids — namely, 

 in the young individuals of a certain group of species of the 

 genus Ophiocoma (0. pumtla, Valenciw). This case is parti- 

 cularly interesting, because it is positively confined to the 

 young individuals, which alone present unequally developed 



* Notes on Radiata, No. 2, p. 205. 



