THEEL, THE AMOEBOCYTES BY ECHINODERMS, 



31 



Taking it for granted that the digitiferous crystals orig- 

 inate in the centre of an amoebocyte as a minute calcified 

 kernel — ef. text-figure 7: 8, I presume this kernel to inerease 

 and gradually aequire the shape of a brightly shining spool 

 — ef. text-figure 7: 9 and plate 3, fig. 1. Thereafter, that part 

 of the cell plasm, which is next to the spool, acquires the shape 

 of a finely granulated rhomboid and becomes calcified and 

 dark-coloured — ef. text-figure 7: 9 and plate 3, fig. 1. Af ter 



4 



fm, 



TvA" 



.^' 



Text-figure 7. 



Developmental stages of crystals from^the coelomic fluid of 

 Cucumaria lactea; drawn from the living. 



1. Globular structureless mother-cell, enclosing a rhomboid in side-view 

 with two parallel surfaces, slightly concaved sides and rounded angles. 

 Diameter = 11,4 ]x. 



2. Similar cell with vesiculous structure; rhomboid biconvex; diameter = 

 15,2 \i.. 



3. Side-view of a rhomboid with parallel surfaces. 



4. Side-view of a biconwex rhomboid. 



5. Globular structureless cell with distinct nucleus and three small refract- 

 ing, calcified grains; it is capable of a certain change of form from glo- 

 bular to oval, causing a slight displacing of the grains. Probably the grains 

 become dissolved again, giving rise to a true rhomboid, an alternate dis- 

 solution and new-formation taking place. 



6. Upper view of a rhomboid with parallel surfaces, concaved sides and 

 rounded angles. 



7. A plasma-amoebocyte evidently preparing itself for the formation of a 

 digitiferous crj^stal, its central rhomboid being ready, and the plasma at 

 the acute angles having separated into two parts; an inner darker and 

 an outer, lighter; contour of the cell indistinct and fading away. 



8. A plasma-amoebocyte containing a central grain, the first trace of a fu- 

 ture crystal. 



9. A låter developmental stage of a digitiferous crystal, the plasma of the 

 cell having separated into three parts: a finely granulated, darker por- 

 tion of rhomboid shape, traversed by an elongated, brightish calcified 

 spool; a frame of light, not fully calcified plasma with processes running 

 out from the acute angles just as is the case in the future digitiform cry- 

 stal; and a surrounding homogeneous plasma. 



