ORGANIC DEPENDENCE AND DISEASE 
77 
“As a rule, a tube occurs more frequently among species in 
which the arms form a continuous series around the calyx, 
while species in which they are arranged in clusters often 
have a simple opening. ’ ’ And it also appears that this tube 
was of convenient rather than essential function. The ani- 
mal could live without it when it was broken oft or ob- 
structed, and easily made a new orifice when necessity re- 
quired. 
2. It appears, however, that early attachment may have 
prevented the development of the anal tube. This would, 
indeed, seem to be indicated by the specimen of C rater o- 
crinus ruedemanni here shown, where the attachment be- 
ginning very early prevented the development of an anal 
tube which would have been normal to this type of struc- 
ture, or at least is normal to all other members of the fam- 
ily to which this belongs — the Dolatocrinidae. 
3. In general, crinoids which have been found to bear 
parasitic gastropods have no anal tube but only a slight 
protuberance. Exceptions to this statement are rare and of 
uncertain value. Actinocrinus verrucosus Hall has an anal 
tube but a specimen is reported by Keyes, with an attached 
snail. 1 In this crinoid, however, it appears that the tube 
has been broken oft and an aperture developed on the dome. 
Waclismutli and Springer refer to Actinocrinus multiramo- 
sus in which this anal tube is retained and a gastropod is 
attached to the tegmen below. 2 
4. The parasitic condition so rampant in these early 
Carboniferous ages disappeared entirely so far as present 
records indicate, with the disappearance of the fauna from 
the various shallow seas of the world. There are instances 
of the continuation of some of these parasitized genera of 
the Mississippian into the marine faunas of the Coal Meas- 
ures (that is, Aorocrinus) but in none is the condition of 
1 Keyes, 1888, pp. 235, 237. 
2 1897, “N. Amer. Crinoidea Camerata, ” p. 566. 
