34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J2 



occurs more or less generally distributed throughout the body just as 

 pigment is distributed throughout the interior of many plants. The 

 coloring matter of the crinoids is, in part at least, a lipochrome, and 

 other lipochromes occur in a number of flowers just as indigo, occur- 

 ring in many different plants, is also found in the Polyzoa and other 

 animals, and just as cellulose or a very closely allied substance is 

 found in the tunicates. 



Many flowers have a sweet and attractive odor, and certain crinoids 

 (Tropionictra and others) also exhale a pleasant plum-like aroma, 

 though this is not so marked as in the case of certain polyzoans 

 (Fiustra) ; as this pervades the whole animal it is perhaps better to 

 compare these types with such plants as those of the families 

 Menthaceae or Myricacese, most of which are aromatic. But among 

 the fixed animals these plants more nearly parallel the sponges in this 

 respect, while the sharp principle pervading the cruciferous plants 

 calls to mind the very acrid secretions found in the coelenterates. 



Many plants, like nettles, have stinging hairs ; in the crinoids the 

 secretion from the glands connected with the hair-like papillae on the 

 tentacles appears to possess stinging qualities. Just as cattle will not 

 eat nettles, so the fishes carefully avoid the crinoids. 



The petals of certain flowers, as in the Hypericacese, are dotted with 

 so-called glands containing excretory products and often arranged in 

 regular rows. Along the ambulacral grooves in the ^rinoids is a row 

 of minute glandular bodies also containing excretory products. 



Similarity of habit and the resultant similarity or at least parallel- 

 ism in the problems to be met have given rise to a very close corre- 

 spondence in many features between the fixed and sessile animals 

 and the plants, though the means by which this close correspondence 

 has been attained differ very widely in the two classes of organisms. 



PARASITES AND COMMENSALS 

 A very large number of organisms belonging to very diverse groups 

 are found more or less associated with the crinoids. The relation 

 between these types and the crinoid hosts runs by imperceptible 

 gradations all the way from true parasitism, in which the organism 

 feeds directly upon the body tissues or fluids of the host, to the most 

 casual or even accidental association. 



The animals associated with the crinoids may be grouped as 

 follows : 



L True parasites. — Animals which (i) live upon the tissues or 

 body fluids of the crinoids and occur either (a) internally or (b) 

 externally; (2) occur internally, though not feeding directly upon 



