125 



It is worth menlioning in this connection that such cases, where rege- 

 neration of an arm after some injury appears to have taken place, are 

 not very rarely met with. 



I may here point out the fact that the metamorphosis in the Ophiurid 

 larvae may proceed after two different types. One is that occurring e. g. 

 in Ophiothri.v and Ophioplutcus opulenliis, where all the inner arms are ab- 

 sorbed, the posterolateral arms alone remaining unaltered, to be cast off 

 on completion of the metamorphosis: in the other type, which appears 

 to be of more usual occurrence, also the right anterolateral arm remains 

 intact, together with the posterolaleral arms, until in a more advanced 

 stage of metamorphosis all these three arms are also absorbed (PI. XXIV, 

 Fig. 3; PI. XXIX, Fig. 3; PI. XXX, Fig. 2). 



It must be left for future researches to find out, whether this remarkable 

 difference has any deeper meaning. I would only here in general emphasize 

 the fact that the metamorphosis of the Ophiothrix-lsava cannot serve 

 to typefy that of all Ophiurids with a well formed Pluteus-larva. Thus 

 e. g. the hydrocoel, in growing to form the hydrocoel-ring, will in some 

 forms start growing from the upper end, in others from the lower end, 

 which certainly makes a considerable difference, both from a morphological 

 and from a biological point of view. Also some conspicuous peculiarities 

 obtain with, at least, the initial stages of metamorphosis in the Ophio- 

 plnfeus bimaculatus-serratus group. 



The fact that in several forms, especially those which keep one of the 

 anterolateral arms intact during metamorphosis, the ciliated band is 

 broken up in pieces, so as to recall the ciliated rings in the Auricularian 

 pupa, may merely be hinted at here. The discussion of its meaning must 

 be left for another occasion. 



Ophiopluteus of Ophiothrix. 



The Ophiothrix-larva is a characteristic, easily recognizable larval type, 

 The posterolateral arms are generally much diverging, sometimes nearly 

 horizontal; they are considerably longer than the inner arms. The body 

 skeleton is simple, with a single small median process from the ventral 

 and dorsal transverse rods. The body rods are mostly thick and robust. 

 The posterolateral rods are slightly thorny along the inner side, the rods 

 of the inner arms have few small thorns. The poslerolateral arms are 

 often conspicuously pigmented. 



Characteristic of this larval type is furthermore the symmetrical position 

 of the developing young Ophiurid. which latter is also peculiar through 

 its ventrally incurved arms with the clawlike spines. The posterolateral 

 arms remain intact during metamorphosis and serve as a floating apparatus 



