36 Hjalmar Théel, 



keeps to the point of one of the arms during its increase. Other me- 

 senchyme cells come to the points of the two remaining arms, suppor- 

 ting them during their increase, and furthermore other cells give origin 

 to the branches or ramifications. 



As may be understood from the above, there is some doubt as 

 to the meaning of Selenka, whether he thinks that the calcareous star 

 retires from the originating cell or not. 



Semon '), who has also occupied himself with this problem, says 

 that the calcareous deposit originates in the interior of a cell as a grain 

 of uncertain shape and that this changes into a tetrahedron. The fur- 

 ther growth goes on mainly in the direction of three axes of the tetra- 

 hedron, the result thus being a regular three-armed star, which Semon 

 now found placed outside the cell and enveloped by a thin homogeneous 

 membrane which he also supposes to have been effected by the calcife- 

 rous cell. Semon doubts whether the calcareous star has escaped from 

 the cell, which he is most inclined to believe, or if it still remains there, 

 the cell itself having lost the nucleus and being transformed into the 

 investing membrane. 



My own researches have led me to the following results. The 

 calciferous cells, which are unenclosed in a definite cell-wall and capable 

 of exhibiting amoeboid movements, contain imbedded in their granular- 

 looking endoplasm, besides various adventitious materials, one calcareous 

 granule or more, the outline of which is uncertain. Besides this plasm, 

 the cells consist of a clear homogeneous hyaloplasm or ectoplasm, to 

 which the more obvious activity of the cell is immediately due; the 

 amœboid movements are produced by a flowing out of this plasm, which 

 extends far beyond the limits of the granular plasm, thus forming the 

 pseudopodia. In a state of rest, when the pseudopodia are withdrawn, 

 the thin peripheral layer of clear plasm hardly appears to surround the 

 cells, which in this condition almost give the impression of being totally 

 granular and well defined, PL I V, fig. 76. 



When the tetrahedron, the first calcareous deposit of a definite 

 form, makes it appearance in Echinocyamus, I never found it enclosed 

 within the granular main portion of the cells, but in the peripheral pseu- 

 dopodial plasm, which has protruded slightly towards the blastoderm, 

 thus appearing as if it were placed outside the cells. As I have already 



1) Beiträge zur Naturgeschichte der Syoaptiden des Mittelmeers. 1887. p. 

 289—295. 



