A MONOGRAPH OF THE EXISTING CRINOIDS 69 



hypertrophied muscle has pressed the dorsal coelome toward the adoral side. Pre- 

 sumably migration of the dorsal hooks toward the aboral side is explained by the 

 stronger calcification and development of the side turned away from the mouth. 



Gislen said that I endeavored to explain the biological function of the combs by 

 assuming that they pick away foreign particles from the arms and pinnules, especially 

 parasitic myzostomes. But he pointed out that the Comasteridae are almost more 

 abundantly provided with these than any other family. He himself found an ento- 

 parasitic IProtomyzostomum on Comantheria delicata grandis, and ectoparasitic myzo- 

 stomes on Comanthus pinguis and Comissia parvula. So he did not think the function 

 of the combs could to any essential extent be the one given by the author. The dif- 

 ferent species of myzostomes are in general each confined to its own particular coma- 

 tulid or to a few species. If the principal task of the combs had been to free the 

 animal from parasitic myzostomes, either these parasites would soon have been rooted 

 out in the Comasteridae, or they would have to become endoparasitic to escape the 

 combs. According to Gislen, in either case the combs as organs for exterminating 

 myzostomes would have become superfluous at about the same time as they appeared. 

 He said that according to this theory it is difficult to understand why certain genera 

 should acquire combs far out on the distal pinnules, for the myzostomes practically 

 always occur on the disk, or on the arms in its immediate neighborhood. For the 

 particles of food become more and more concentrated toward the mouth. Still, 

 Gislen said, there is a possibility that in certain forms the combs have a general cleansing 



function. . . 



Gislen maintained that the dorsal hooks in comasterids with reduced cirri act 

 as anchoring organs offsetting the loss of the cirri. He noted that this seems to be 

 the case also with the grooveless pinnules in Comatulella brachiolata and remarked 

 that in these the coiling takes place more toward the laterodistal side than toward 

 the dorsal side. He found this theory supported partly by the occurrence of the 

 dorsal hooks, so generally and exceptionally strongly developed in the Comasteridae, 

 and partly by the reduction and disappearance of the cirri in certain species. In 

 Comanthus pinguis the cirri are strong and the dorsal hooks weak, and in Comanthus 

 timorensis the conditions are reversed. 



His idea of the development of the teeth of the combs from the dorsal hooks is 

 as follows: Originally all the distal segments of the pinnules possessed small dorsal 

 hooks. Dorsal hooks appear in a more or less rudimentary form on the outermost 

 segments of the more distal pinnules in most of the comatulids. On the other hand, 

 the oral pinnules are smooth distally except in the subfamily Hehometrinae of the 

 family Antedonidae. 



The combs must be considered to have appeared first on the oral pinnules. In 

 forms in which the combs extend far out on the distal pinnules this feature appears 

 only at an ontogenetically very late stage. 



The oral pinnules in most of the comatulids are developed into tactile organs 

 and are very sensitive. In a number of forms, thanks to short segments, they are also 

 exceedingly flexible. Because of the formation of the facets of the segments this 

 flexibility can function only in a lateral direction. Thanks to the dorsal hooks and 

 the great flexibility of the oral pinnules, the latter were able to catch hold of objects 

 falling upon the disk or outside the ambulacral grooves that were too large to be 



