Evolution and Symmetry in the Order of the Sea-pens. 123 



systematic purposes, even in the higher Pennatnlids, as it is possible that 

 differences may be found in some cases in the spicular armature of young 

 and old colonies. Thus Grieg has shown that, in young colonies of 

 Funiculina quadrangidaris* spicules are present in the tentacles of the young, 

 but not in the tentacles of the old colonies. In other cases the spicules 

 seem to be more numerous and widely distributed in the older colonies than 

 in the younger ones. 



Moreover, if the spicules of any particular part of the rachis, such as the 

 dorsal track, the calyx of the siphonozooids, the outer border of a leaf, or the 

 tentacles be examined in a iiumber of specimens of a given species, it will be 

 found that they are constantly of the same form and approximately of the 

 same size, although occasionally local variations are found in the number and 

 size of the spicules in the zooids, due perhaps to local environmental 

 conditions. An interesting example of such a local variation in the spicules 

 was found in the examination of three specimens of P. fimbriata from 

 the coast of Timor and two specimens of the same species from the Kei 

 Islands. The species is an interesting one, as being intermediate in many 

 respects between the two genera Leioptilum and Pennatula, and one of the 

 distinguishing features given by previous authors of the genus Leioptilum is 

 that spicules are confined to the margins of the leaves, whereas in Pennatula 

 they are more evenly distributed throughout the whole leaf. In two 

 specimens of P. fimhriata from the Kei Islands the spicules are confined to 

 the margins of the leaf as in Pennatula, but in the three specimens from 

 Timor these marginal spicules are supplemented by others, extending almost 

 to the base of the leaf. The spicules of the Timor specimens, moreover, are 

 much larger and more numerous throughout the colony than in the specimens 

 from the Kei Islands. Many other instances, probably, could be found of 

 local variations of the spicular armature of the higher Pennatulids, but such 

 instances ought not to obscure the much more impressive fact of the 

 constancy of these characters in specimens taken from a single locality, and 

 the remarkable similarity, in most cases, as regards this character, seen in 

 specimens from distant localities, when the higher Pennatulids are compared 

 with the radially symmetrical Veretillidse. 



There is one more character frequently used in systematic treatises that 

 may be briefly referred to before passing on to a more general statement. If 

 a large number of specimens of a species of Pennatula from a single locaUty 

 be carefully measured, it will be found that the ratio of the length of stalk 

 to length of rachis is fairly constant. For example, in 38 specimens of 

 P. ■phosphorea, var. candMa, from the Mediterranean Sea, the ratio of 

 * Giieg, ' Bergens Museums Aarbog,' 1896. 



VOL. XC. — B. L 



