

5TSKRIFT FOR LILLJEBORO 



10 



Furthermore, seeing that simultaneously one of the apical plates of the future 

 sea-urchin takes its origin as a minute three-armed spicule close to the hinder portion 

 of the pluteus, the study of the relation between the calciferous and absorbent cells 

 is highly promoted. Indeed we arc here able to see how the cells in question, though 

 opposed in their functions, intercommunicate by longer or shorter plasmic threads, 

 which often arrange themselves in a meshwork. The salts in fluid form are gradu- 

 ally transferred through the pseudopodial threads from one part of the pluteus, where 

 the skeleton becomes impeditive for the farther evolution of the larva, to another 

 new centre of calcification, where the operative cells arc in need of material for build- 

 ing up new calcarious bodies. 



In such places of the broken spicules where the "body" of an absorbent cell 

 has settled for some time in order to exercise its absorbent influence, small shallow 

 pits may be found which are probably identical with "Howship's foveolae" in verte- 

 brates. 



The annexed wood-cut No. I represents the hinder portion of a pluteus of Echinus miliaris 



drawn from a living specimen, a, ciliated hand bordering the posterior, slightly curved outline of the body. 



i supporting rods having their ends broken, c, the broken end-pieces almost keeping their original 



ion in the larva and considerably remote from the main parts of the rods, d, a three-armed spicule 



mounded by a heap of calciferous cells, representing an early stage of a future apical plate, e, the out- 



: sea-ur« hin. /, the stomach of the pluteus. 



The dotted lines in the figure show the meshwork of pseudopodia and cells 

 through which the dissolved salts are transferred from the broken end-pieces to the 

 ew centre of calcification (<•/) as well as to the out-growing sea-urchin, both of which 

 liri calcarious salts in abundance. 



