The Crinoids from Dr. S. Rock's Kxpedition to Japan 1014. 177 



full-grown specimen therefore continues the length-growth of the stem, 

 but the diameter of the stem is very little or not at all increased and 

 might (in old specimens ?j even decrease. An full-grown M. interruptus 

 migth thus have a total stem-length of 2 — 2,5 metres, but from 

 what is mentioned above it is probable that in older specimens it 

 might be considerably lai-ger. The previously described specimens of 

 M. rotiindus probably have much longer stems, foi- these only show an 

 inconspicuous or no increase of the diameter. The fact that large 

 specimens exhibit a decrease of the diameter of the stem (cf. M. rotun- 

 dus Sp. 4, M. interruptus Sp. 21) has also been observed by Doderlein 

 (Siboga Exp. Vol. 42 A, p. 29 ff.). I have not established any periodi- 

 city in the growth of the stem-diameter in M. inlerruptus. 



The proximal segments of the cirrals are short and discoidal, 

 but the number of these short segments is evidently a function of 

 the age of the animal. In e. g. Sp. 16 cirral 2 is already as long as 

 broad, in Sp. 17 the 3^ in Sp. 18 the 4"\ in Sp. 14 the 5'\ m Sp. 5 

 the 6"\ in Sp. 6 the 7* and in Sp. 10 the 9"' segment is cubical. In 

 the corresponding specimens the number of cirrals and their L are 

 on an average 20(10 mm.), 23(12 mm.), 31 (20 mm.), 33 (22 mm.), 

 42(35 mm), 41 (38 mm.), 42 (43 nmi.). — The distal cirrals are, as in 

 the comatulids, longer in younger specimens; e. g. Sp. 16 has the L 

 of the 4"'— 8"' cirrals = 2 br (cf. Sp. 3), The same prolongation is also 

 seen in the stem-joints, which in the youngest specimens are longer 

 than broad. Therefore the cirrus-sockets on the nodals in the young- 

 specimens do not reach the proximal border. 



The interarticular pores cease very constantly at the 7"' or 8"', 

 in some rare cases in large specimens (10, 10, 20, 21) not until the O**^ 

 or 10"' internodes. In the very young specimens 14 — 17 the pores 

 have disappeared already at the 2'' to 6*'' internodes — a manifesta- 

 tion af more rapid stem-growth. 



Full number of internodal joints in the largest specimens (6, 10, 

 11, 19, 20. 21) appears in the (5*— )6'h^-7"' internodes, on the other 

 hand in tiio smallest specimens already in the (4"' — 13'' or even in the 

 first internode (Sp. 3, 13—18). 



Sperry has doubted whether M. mtmuhis and M. mterruptns 

 should be considered as diffei'cnt species. 1 grant he is right inas- 

 much as there is no essential difference in the number of components 



Nova Acta Reg. Soc. Sc. Ups.. Ser. 4, Vol. 5. N:o fi. Impv. "i 1922. 23 



