124 



Prof. S. J. Hickson. 



stalk-length to rachis-length was about 1 : 1'5, the range extending to 

 1 : 1"9 and 1 : 0'8. In nine specimens of the same species, var. variegata, 

 from the coast of- Denmark, the range extended from 1 : 1-86 to 1 : U.S. 

 In 33 specimens of P. pearceyi from the coast of East Africa, the 

 range extended from 1 : 1'7 to 1 : 3"2 (Kiikenthal and Broch). In six 

 specimens of P. murrayi from the coast of Timor, the range extended from 

 1 : 3'6 to 1 : 5"5, and in four specimens of the same species from the Kei 

 Islands from 1 : 2 to 1 : 4. All the specimens of P. phosphorea were obtained 

 in shallow water (150 metres), the specimens of P. pearceyi in deep water 

 (693-1134 metres), the deep-sea forms in this case having a shorter stalk. 



The specimens of P. murrayi from Timor were obtained in shallow water 

 (112 metres), and those from the Kei Islands in deep water (310-397. 

 metres), the deep-sea forms in this case having a longer stalk. 



A consideration of these ratios and others that have been worked out leads 

 to the conclusion that, even in the genus Pennatula, the stalk-rachis ratio is 

 not a very reliable character for the determination of species, and, further, it 

 seems to indicate that the rachis is much more variable in deep-sea species 

 than in shallow-water species. Whether the relatively short stalk in 

 specimens of P. murrayi from deep water is to be correlated with depth or 

 with the character of the sea bottom is a matter that requires further 

 investigation. Nevertheless, through all the conflicting evidence afforded 

 by these measurements, it seems that the specimens of a given species living 

 under the same conditions of depth and sea bottom have in this genus, at 

 least, a ratio of length of stalk to length of rachis that varies within a small 

 range from a common average, and this conclusion is confirmed by the 

 measurements I have made of 30 specimens of S. m<irte)isii from the 

 same locality off' the coast of Timor, in which the length of the stalk was 

 about 4i\ times the total length of the colony. In the radially symmetrical 

 Veretillidaj it is difficult to obtain trustworthy estimates of this ratio, 

 because specimens seem to suffer more from contraction during preservation 

 than specimens from the genera with a complete axis. Neidermeyer found, 

 however, that in V. cynomoriam no two species possessed the same ratio of 

 length of stalk to length of rachis, and my own impression, from the study 

 of this family, is that the character is much too variable, even in specimens 

 from the same locality, to be of any value for systematic purposes. 



Having now discussed in some detail the differences observed in the 

 variability of certain individual characters, it is necessary to turn to the 

 characters as a whole of the genera and species to ascertain if their study 

 confirms the conclusion already indicated. It mi^ht be anticipated that if 

 the individual characters in any one group are more variable than in another 



