CRINOIDEA. 265 



therefore, there is an extremely important distinction be- 

 tween the older types of Crinoids and the later ones, though 

 the process by which the microscopic organisms which serve 

 as food are collected from the surrounding water and con- 

 veyed to the mouth, seems to have been in both cases essen- 

 tially the same. Moreover, even in the living Antedon, as 

 shown by Dr Carpenter, the true mouth is situated at a 

 little distance below the apparent mouth, as formed by the 

 point of convergence of the brachial furrows ; so that if we 

 imagine these furrows to be roofed over by calcareous plates, 

 where they cross the ventral surface of the disc, we should 

 have a condition of parts closely resembling what we find in 

 the Palgeocrinoids. 



The stalked or " pedunculate " Crinoids of the present day 

 are few in number, and are mostly inhabitants of the deep 

 sea. We find, however, various and widely distributed rep- 

 resentatives of another group of Crinoids namely, the 

 " sessile " Crinoids, all of which are generally known as 

 " Feather-stars." In all these, such as the living Comatula, 

 Antedon, Actinometra, &c., and the extinct Saccosoma (fig. 

 156) and Solanocrinus, the animal is only stalked when 

 young, and in its adult condition leads a free life. The 

 young form in the members of this group is supported upon 

 a jointed calcareous column, by which it is fixed to some 

 foreign object ; and at this stage it in no respect differs from 

 the ordinary stalked Crinoids. At a certain period of its 

 existence, however, the calyx drops oif its column, and 

 becomes a locomotive animal. It now has a near resem- 

 blance to one of the Brittle-stars (Opkiuroidea) ; but is dis- 

 tinguished, not only by its developmental history, but also 

 by its internal and skeletal structure, by the possession of 

 lateral pinnae to the arms, and in having the reproductive 

 organs situated external to the body proper. In the Feather- 

 stars, moreover, the dorsal surface of the disc, at the point 

 where the column was originally inserted, carries a series of 

 jointed filaments or " cirri," by which the animal can moor 

 itself to any foreign object. These may be regarded as 

 homologous with the " side-arms " of the column of certain 

 Crinoids. When the animal is thus temporarily moored 



