

CHAP, ix.] THE DEEP-SEA FAUNA. 445 



A young specimen of P. ivyville-thomsoni gives the 

 mode in which this freedom is acquired. The total 

 length of this specimen is 95 mm., of which the head 

 occupies 35 mm. The stem is broken off in the 

 middle of the eighth internode from the head. The 

 lowest complete internode consists of 14 joints, the 

 next of 18, the next of 20, and the next of 26 joints. 

 There are 8 joints in the cirri of the lowest whorl, 

 10 in those of the second, 12 in those of the third, 

 and 14 in those of the fourth. This is the reverse of 

 the condition in adult specimens, in all of which the 

 numbers of joints in the internocles, and of joints 

 in the cirri, decrease regularly from below upwards. 

 The broken internode in the young example, and 

 the three internodes above it, are atrophied and un- 

 developed, and suddenly at the third node from the 

 head the stem increases in thickness, and looks as 

 if it were fully nourished. There can be no doubt 

 that in early life the crinoid is attached, and that it 

 becomes disengaged by the withering of the lower 

 part of the stem. 



The structure of the cup is the same as in P. 

 asteria and P. mulleri. The basals appear in the 

 form of shield- like projections crowning the salient 

 angles of the stem. Alternating with these we have 

 well-developed first radials, forming a closed ring 

 and articulating to free second radials by muscular 

 joints. The second radials are united by a syzygy 

 to the radial axillaries, which as usual give off each 

 two first brachials from their bevelled sides. A 

 second brachial is united by syzygy to the first, 

 and normally this second brachial is an axillary, 

 and gives off two simple arms ; sometimes, however, 



