. Echinoidea of the Swedish South Polar Expedition. Sea urchins. 80 TH. MORTENSEN, (Schwed. Siidpolar-Exp. be taken into account any more in serious scientific discussions. — It may be ob- jected that the figure represents A. cordatits, while my observations are made on A. cavernosas, and that the differences might thus be due to specific differences. This objection does not hold good, for two reasons: I) it is extremely improbable that two so nearly related species as A. cordatus and cavernosas should prove so highly different in this early stage, and 2) I have examined a corresponding stage
. Echinoidea of the Swedish South Polar Expedition. Sea urchins. 80 TH. MORTENSEN, (Schwed. Siidpolar-Exp. be taken into account any more in serious scientific discussions. — It may be ob- jected that the figure represents A. cordatits, while my observations are made on A. cavernosas, and that the differences might thus be due to specific differences. This objection does not hold good, for two reasons: I) it is extremely improbable that two so nearly related species as A. cordatus and cavernosas should prove so highly different in this early stage, and 2) I have examined a corresponding stage of A. cordatns and found it exactly agreeing with A. cavernos7is. Pedicellariae are developed already in this stage, both globiferous, rostrate and tridentate, the latter both 2- and 3-valved; they are all of the same structure as in the grown specimens; the rostrate pedicellariae are only comparatively very large. The disk of the tubefeet of the frontal ambulacrum is small, the rosette plates are not yet developed. The tubefeet around the mouth show the first indication of the terminal prolongations. The spicules are few and small. The next stage, the youngest of the free- living specimens found in the material, is repre- sented by specimens of 4 mm. length. There is thus a small gap here. Meantime the develop- mental processes, which have been going on while the specimens have grown from mm. to 4 mm. length, are easily enough understood. There is a complete series of specimens of the following sizes. In PL IX are represented a series of figures of young specimens (4, 5, , 6, , 7, 8, , 9, 12, 16 and 18 mm.) showing the changes under- gone by the test during growth. The tests have been cleaned and treated with alcohol-glycerine and show the limits of the plates upon the whole very clearly. It has, however, been thought necessary also to give some text-figures illustrating the minor features, which cannot be seen exactly in the phototypic plates, but which are ne-
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1910
