HJALMAR THÉEL: ACTIVITY OF AM. .K]:. .11, CELLS IN THE ECHIN 



proving the plasm to be in a state of laborious activity. I have n<>. 



live cell escape the spicule till the absorption of h ,g that the 



attacked calcareous particle is often of considerab npared with th 



boid cell, one is led to suppose the latter capable of dissolving an unex 



quantity of salts and of keeping them in fluid form evidently without their solidify 



in the form of granules or other calcareous particles within the plann. I: r, it 



seems to me more likely that the dissolved salts are transferred gradually through the 



pseudopodia to the cells in the neighbourhood which either may retain them until 



necessity requires otherwise or use them immediately as materials for building up 



new calcareous bodies or organs essential for the growing Echinoderm." 



During my stay at our Swedish marine biological station during the 

 two summers, I had unsought opportunities of resuming my researches on the ab- 

 sorption of the larval skeleton in the pluteus of Echinus miliaris. 1 paid special atten- 

 tion to the mode of operation of the wandering cells, whether they retreat from the 

 attacked spicule when filled with a sufficient quantity of dissolved My 



repeated investigations confirm my former views. The cells do not release the 

 cule, or at least, their peripheral, pseudopodial plasm never loses its connection with 

 it, before it is completely absorbed. 



When the pluteus has reached its third stage of growth, being then provi 

 with fine centres of calcification, the back portion of the body retains for some time- 

 its elongate, conical shape and is supported by the rods of the two first protruding 

 arms. The posterior part of these rods which meet at the posterior point of the body, 

 is enlarged and more or less distinctly club-shaped. During the increase of the young 

 sea-urchin, the hind portion of the pluteus gradually changes from conical to rounded, 

 almost half-spherical, and lastly assumes a broad, rectangular shape with the 

 terior outline almost straight. Meanwhile, that part of the ciliated band which ai 

 panies the arms on each side of the pluteus, by degrees travels backward, and is 

 finally found bordering each end of the posterior outline of the body. 



Such thorough changes in external appearances are, however, not o ncci- 

 vable unless the posterior end of the rods in question becomes absorbed, thei 

 making it easier for the remaining main portion of the rods to take a position more 

 suitable to support the pluteus in its new shape. In most cases, if not always, I have 

 also seen, at a certain period of the development, the ends of the rods br< 

 and enclosed within an absorbent plasm. The fraction is probably facilitated by the 

 dissolving influence of one or several cells. In all cases, we have here th 

 favourable opportunity of studying the process of absorbtion and the mode ition 



of the absorbent cells. 



