On Arachnactis hrachiolata. 



527 



at one extremity of the longitudinal axis of the mouth we 

 find the oldest tentacles, while at the other, tentacles are 

 constantly added which belong to one and the same cycle, 

 although not all formed at the same time. Besides these 

 tentacles which are all in pairs, an odd tentacle is devel- 

 oped opposite the extremity of the mouth nearest the edge 

 of the disk. (Fig. 3.) 



The disk of specimens having as many as sixteen ten- 

 tacles, (fig. 2,) is very elliptical, the whole body being 

 strongly compressed laterally in the same direction as the 

 slit of the mouth. (Fig. 3.) So that, when seen from the 

 narrow side facing the odd tentacle or the youngest pair 

 of tentacles, the appearance of the animal is quite different. 

 In the first case the tentacles are arranged symmetrically 

 on both sides of the small odd tentacle, (fig 4,) an uneven 

 number of tentacles being seen ; while 

 in the second case there is an even 

 number of tentacles seen arransfed on 

 both sides of the prolongation of the 

 longitudinal axis of the mouth, as in 

 fig. 2. When seen from the broad 

 side the aspect is still different, the 

 tentacles decreasing regularly in size, 

 after the second pair, from the extrem- 

 ity where the odd tentacle is placed 

 towards the part of the disk where the 

 new tentacles are added. (Fig. 5.) 

 This figure has only three pairs of ten- 

 tacles, but the proportions of the dif- 

 ferent tentacles always remain, in the 

 specimens which I have seen, nearly 

 like this, as can readily be seen from 

 figure 2, which has six pairs of tenta- 

 cles. When seen from the narrow 

 side, the large tentacles are placed Figure :i from tue broaa 

 symmetrically on both sides of the disk. 



Tentacles of fig. 2 from the 



narrow side ficiui; odd 



tentacle. 



ide. 



