22 THE VOYAGE OF H.M.S. CHALLENGER. 



ones just beneath the calyx. Throughout its whole length it tapers downwards from 

 the calyx, rapidly at first, then more slowly and afterwards somewhat rapidly again, 

 till the joints are but little larger than those of the most developed cirri on its middle 

 part. The number of internodal joints also diminishes in this lower part of the stem ; 

 for while it i-eaches eleven or twelve in the middle of the stem, the numbers in the four 

 lowest internodes are respectively nine, seven, five, five ; and the remains of the cirri borne 

 at the intervening nodes show a corresponding diminution in size. The inferior termi- 

 nation of the stem is not known, as it is broken at the syzygy beneath the lowest whorl 

 of cirri. 



The free mode of life appears to be attained in these individuals, not by actual 

 fracture of the stem at a node so as to shorten it more or less, but by the lower and 

 therefore older part remaining undeveloped, while new joints appear in succession above 

 it, each growing to a larger size than those previously formed. The stem thus becomes 

 slender and tapering, and but ill adapted for attaching itself below ; but its length 

 is not diminished so much as if it were broken at a node. 



The downward tapering of the stem in some of the fossil Pelmatozoa has been 

 already noticed ; and it is evidently a character of more general occurrence than 

 was suspected by Sir Wyville Thomson. Quenstedt^ contrasts the comparatively 

 short tapering stems of Extracrinus briareus with the gigantic ones of Extracrinus 

 subangidaris, which may reach the length of 50 or even of 70 feet ; and he 

 suggests that the former type and its allies " konnten gleichsam als eine Comatula 

 betrachtet werden, deren Knopf zu grosserer Lange in einer Zeit heranwuchs, wo es 

 noch keine eigentlichen Comateln gab." De LorioP in like manner regards it as 

 probable — " qu'ils avaient, h I'etat adulte, une tige court, libre, et qua I'aide de leurs 

 cirrhes tres nombreux et tres longs ils pouvaient nager facilement et se transporter, 

 rapidement peut-etre, d'un lieu h, un autre ; ils avaient aussi la faculte de se fixer a 

 quelque objet, lorsqu'ils en avaient le desir, au moyen des crochets dont est munie 

 Fextremit^ de leurs cirrhes." 



I suspect, however, that the swimming was efi"ected rather with the arms than with 

 the cirri, which are not used for that purpose by the Comatulte, and would have to 

 be moved with considerable power in order to efi"ect the locomotion of the animal. 

 The condition of so many recent species is a strong argument in favour of the views 

 formerly expressed by Buckland ^ and others regarding the possible locomotive powers 

 of the Liassic Pentacrinidae, though they have been somewhat discredited of late. Now 

 too that their recent representatives have been found so abundantly in depths of less 

 than 100 fathoms, instead of being exclusively abyssal ty|)es as was once supposed, the 



1 Encriniden, p. 271. 



2 Notice sur le Pentacrinus de Sennecey-le-Grand, Clialon-sur-Saone, 1878, p. 12. 

 ' Geology and Mineialogy, vol. i. p. 437. 



