8 HJALMAR THEEL, NOTES OX THE DEVEEOPMEXT OF ECHINOCARDIUM AXD PARECHIXUS. 



fication gradually extend and increase owing to other calciferous cells associating and 

 fusing together by longer or shorter, coarser or finer plasma-threads. 



The ultimate result of all these operations is the formation of two amoeboid 

 syncytia which gradually take the form of the two future rods and, so to say, direct 

 the gradual formation of the calcareous rods in question. 



In short, I entertain the opinion that the syncytia in question serve as a kind 

 of moulds which predetermine the shape of the gradually arising calcareous rods, and 

 that the numerous small lateral spines of these rods are due to short pseudopodial 

 protrusions of the syncytia. 



To sum up, the original amoeboid cells, which have disengaged themselves from 

 the combination of cells which constitutes the vegetative pole of the larva, have becn 

 subjected to a change of functions. A part of them still remain true amoeboid cells 

 of a stellate appearance which move within the larval cavity and are capable of 

 forming small temporary meshwork by the junction of their pseudopodia; låter on 

 they may remain free, or partake of the formation of tissues and, consequently, lose 

 their relative freeness. 



Another part of the wandering cells become immediately transformed into calci- 

 ferous cells which communicate with other cells of the same kind and form syncytia 

 which increase and gradually aquire the shape of the future calcareous rod. These 

 syncytia have the function of taking up calcareous salts in fluid form from the sea- 

 watcr and solidifying them, thus giving rise to the larval calcareous skeleton. The 

 fäte of these calciferous syncytia is mysterious ; considering that the Echinodcrms dur- 

 ing their whole term of life are in need of calcareous salts in great quantities, they 

 probably remain calciferous. 



Finally we have to note a third kind of cells, the absorbent ones, which form 

 syncytia too, but differ from the former by possessing the power of absorbing and 

 destroying such parts of the larval skeleton which are unsuited for further evolution 

 of the larva. The appearance of absorbent cells and the process of desl ruction take 

 place when the larva is in need of great er quantities of calcareous salts, that is to 

 say w lien the pluteus has attained its tnature state. »At this period of the develop- 

 ment not only plates and spines but even pedicellaria, pedicels, sphseridia and theeth 

 vvith their alveoli begin to arise almost simultaneously, all these organs requiring 

 calcareous salts in abundance. Under such eiremnstances it must be verv suitable 

 if not a necessity to have a supply of calcareous substances in reserve within the 

 body.» 1 



Finally, I cannol pass över in silence the marvellous facl that these two kinds 

 of syncytia, the calciferous and the absorbent , appear to eooperate and to fnse to- 

 gether by t lic union of their Longer and shorter pseudopodial prol rusions. Thus 

 in these composcri syncytia the uiain granular portion of their cells perform quite 

 different functions. The above remarks may be sufficient to provc Ihat the ab- 

 BOrption and dest ruction of the skeleton in the Kchinodcrms go on hand in hand 



1 Tim i., i.,,- , ,t . p. :\:,-2. L894. 



