MONOGRAPH OF THE EXISTING CRINOIDS. 613 



be found in the digestive tube, together with the frustules of diatoms, spores of 

 algae, etc. In sections of Bathycrinus, Rhizocrinus, Isocrinus, and Endoxocrinus 

 from deep water the silicious skeletons of radiolarians may be found in consider- 

 able abundance and variety. Foraminifera, too, form a staple article of food for 

 these deep-sea species, for he frequently found Globigerina, Biloculina, and other 

 types beneath the covering plates of the food grooves on the arms and pinnules, 

 while the remains of their sarcode bodies occur in the intestines of decalcified 

 specimens. 



Seeliger believes that he recognized in the earliest food of the larvae half 

 digested infusorians and different pelagic larvae. 



Bury found the stomach of the early pentacrinoids so filled with diatoms that 

 the cutting of sections was rendered very difficult. 



Dr. Edwin Kirk states that in the case of a number of specimens of C'omanthus 

 japonica which he examined the contents of the intestine were almost wholly com- 

 minuted animal matter. 



At Maer Island, Torres Strait, Dr. H. L. Clark examined the stomach contents 

 of four comatulids (species undetermined). He found that in each case the 

 greater part of the food material was green algse, chiefly unicellular, though some 

 linear forms (thread algse) were also noted; a few diatoms were detected, and 

 some foraminifera. In one of the stomachs several radiolarians were seen, in 

 another a piece of a red alga, and in a third some fragments of minute crustaceans. 



Doctor Clark also examined the stomach contents of Tropiometra picta at 

 Tobago, which he found to consist of a mixture of vegetable and animal food, the 

 former predominating. The plants were diatoms and unicellular green algse, with 

 occasional fragments of seaweeds; of animals, crustaceans were most frequently 

 noted, but a few foraminifera were also seen. The crustaceans were minute 

 amphipods, copepods, and crab zoseas. 



Dr. Th. Mortensen found that a relatively large percentage of the penta- 

 crinoids of Isometra vivipara have in their stomachs the half-digested, but still 

 perfectly recognizable, remnants of larvae; he even found very young penta- 

 crinoids with the vestibule recently ruptured and the arms not yet developed with 

 embryos almost as large as themselves in their mouths. 



He remarks that, on account of the large number of pentacrinoids found 

 attached in clusters to the tips of the upturned cirri as many as 99 in one speci- 

 men this danger to the embryos is very real, and probably quite a large number of 

 them perish in that way. 



PARASITES AND COMMENSALS. 



A very large number of organisms belonging to very diverse groups are found 

 more or less intimately 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 accidental association. 



The animals associated with the crinoids may be grouped as follows : 

 I. True parasites : Animals which (1) live upon the tissues or body fluids of the 

 crinoids and occur either (a) internally or (b) externally; (2) occur internally, 



