500 W. WOODLAND. 



outline towards the circular margin and speedily assumes a 

 star-shaped form. The tubular rays of the star which grow 

 out are equal in calibre and meet the external membrane, 

 arching forwards somewhat at the points of contact. The 

 longitudinal extension of the radially-arranged outgrowths 

 keeps pace with the increase in the size of the cell, and finally, 

 when the cell attains a size of fi'om O'OG mm. to 0'07 mm., 

 the rays become united by a peripheral membranous ring. It 

 is now impossible to mistake the mould of the subsequent 

 calcareous wheel, prepared as it is by the complex folds of an 

 internal membrane ; the central portion with the cluster of 

 nuclei corresponds to the nave, the tubes running out like the 

 rays of a star represent the spokes, and the peripheral ring 

 takes the place of the circumfei-ence (the felly) of the future 

 calcareous wheel. Moreover the calx is actually secreted 

 into this organic matrix formed by the skeletogcnous cell, as 

 into a mould, and in such a way that (as the older accounts 

 already teach us) calcification takes place first in the nave, 

 then in the spokes, and finally in the felly of the wheel. It 

 is likewise in accordance with the theories which have recently 

 been formulated as to the share of the nuclei in the vital 

 processes of the cell that, corresponding with the centrifugal 

 progress of the calcification, the majority of the cell-nuclei 

 also separate from one another in a centrifugal direction, and 

 in the case of the Auricularia3 from the Canary Isles come to 

 lie in the acute angles between the spokes. In rare instances 

 they advance as far as the middle of the spokes, or even to the 

 peripher3\ No secondary multiplication of the spokes of the 

 wheel takes place ; their number corresponds exactly with 

 that of the undulating evaginations of the newly-formed 

 internal membrane, which develop into radiating tubes. As 

 is well known, the number of the spokes varies; in the case 

 of the Auricularifc from the Canaries, we find from thirteen 

 to eighteen. Since the diameter of the fully-formed cal- 

 careous wheels is found to be from 0'09 mm. to 0*1 mm., it 

 follows that a ten-fold enlargement of the diameter of the 

 skeletogenous cells takes place, since the latter in the stage 



