30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J2 



order to obtain an adequate supply of these organisms they must 

 intercept the maximum amount of water without, however, impeding 

 its flow, for it must pass by them constantly and continuously in order 

 to furnish them with a supply of oxygen without which they would 

 soon perish, as well as to deliver to them the requisite amount of 

 food. As the maximum area is included within a circle the crinoids 

 have developed a circular food-collecting apparatus consisting of 

 slender pinnules which, spread out in the form of a circular net, 

 filter the maximum amount of water while at the same time they 

 interrupt the flow of water to the minimum degree. In this circular 

 food-collecting apparatus composed of a vast number of slender 

 filaments we see at once the influence of the same factors which have 

 determined the development of the submerged filiform-dissected 

 leaves among the water plants ; and the similarity becomes more strik- 

 ing still when we call to mind such carnivorous plants as the species 

 of Utricularia. 



The crinoid crown is almost entirely a food-collecting apparatus ; 

 the essential organisms of the animal are reduced to a minimum and 

 subordinated to the development of a structure offering a maximum 

 area for the interception of food particles. This is not by any means 

 a peculiarity only of the crinoids, for all of the other fixed and 

 arborescent animals, the sponges, coelenterates, polyzoans, tunicates, 

 protochordates, etc., have similarly subordinated, as it were, their 

 whole being to the specialization of the mechanism for collecting 

 mobile food to such a degree that they may be differentiated often 

 down to genera, and sometimes even down to species, by the char- 

 acters found in the food-collecting apparatus alone without considera- 

 tion of their other structures. The polyp or polypoid individual more 

 or less flower-like in form or else capable of maintaining a strong 

 inflowing current of water is a physical necessity correlated with a 

 fixed existence, and the contrast between the requirements of a fixed 

 and an active life are nowhere better illustrated than in the echino- 

 derms through the comparison between the crinoids on the one hand 

 and the echinoids, asteroids and ophiuroids on the other. 



Terrestrial plants live rooted in the earth from which and from the 

 surrounding atmosphere they derive all the substances necessary for 

 their existence. But the medium about them is so light that some 

 special provision must be made for the fertilization of their ova. 

 Thus while the crinoids, and all the other fixed marine animals, have 

 had to specialize, so to speak, on the development of an adequate 

 apparatus for food collection, the plants have had to devote their 

 energies to the problem of securing cross fertilization. This is largely 



