KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 49. NIO 4. 5 



I. The aclivity of amoeboid cells of Echinid larvos. 

 II. The develoyment of the Hydrocoele ring. 



I. In dealing with the amoeboid cells, I do not take into consideration the 

 rest of the corpuscles which are to be found in the perivisceral cavity of the more 

 advanced Echinids, viz., påle and brown granular corpuscles and small globular cells 

 with a long vibratile cilium, of which the granular ones at least must be derived 

 from the true amoeboid cells. 1 



The amoeboid cells play a significant part in the vital process of the Echinid 

 life, in the developmental stages as well as in the more advanced stages, and are 

 known by the name of migratory or wandering cells, leucocytes, påle or colourless 

 corpuscles, lymphoid cells and also phagocytes. They take their origin from the 

 vegetative pole of the larva at a rather early period, lose their connection with sur- 

 rounding cells, and immigrate into the blastocoel as free wandering cells. The sepa- 

 ration of such cells from the walls of the invaginated portion is going on during the 

 whole process of gastrulation, and they generally present fine pseudopodial filaments 

 connecting the ectoderm of the gastrula with the archenteron. 



Låter on, in more advanced stages of the development and metamorphosis a 

 multiplication of them evidently must take place by division too. 



As soon as these cells have löst their connection with the layer of cells which 

 constitute the vegetative pole and the entodermic invagination and immigrated into 

 the body cavity, a differentiation of them evidently takes place. Some of them still 

 remain true amoeboid cells, while the rest change into what might suitably be ter- 

 med »osteoblasts > and »ostoclasts», the former being calciferous, the latter, on the 

 other hand, having the function of absorbing calcareous particles. Evidently a re- 

 markable change of functions has taken place here. 



With regard to those cells which remain true amoeboid or migratory, they in- 

 cessantly change in form and position. 



Owing to rather long pseudopodia which anastomose with protrusions of other 

 cells and even with the cells of the lar val body-wall itself, they of ten exhibit a kind 

 of meshwork in the cavity of the larvse. Considering, however, that the pseudopodia 

 become withdrawn again and lose their connection, such a meshwork, or rather syn- 

 cytium, is only to be looked upon as temporary, never as fixed. Tims, according to 

 my opinion, the cells in question are incessantly changing in order to bring forth 

 new pseudopodial combinations. 



However, Mac Bride 2 seems to hold a different opinion, when he writes as 

 follows: »These mesenchyme cells were of two kinds: (1) aggregated masses of roun- 

 ded cells, which formed the matrix of the future larval skeleton, (2) wandering cells 



1 Cuénot, Arcbives de Zool. Exp. et géuérale. Ser. II. T. 9. 1891. p. 614. 



- Xote on the continuity of meseuehyme cells in the Echinid larvae. — Proc. Thil. Soc. Cambridge. 

 Vol. 9. 1896. 



