Modifications in Development of the Sand Dollar by NaCNS

Abstract

Experiments conducted at the Hopkins Marine Station, Pacific Grove, California, during the summer of 1938 on the unfertilized and fertilized eggs of Dendraster excentricus have given certain interesting modifications in the early developmental patterns of this form.

Unfertilized eggs treated for 12 hours with a solution of NaCNS (20 cc .54 M NaCNS plus 100 cc Ca-free sea water) showed a retardation in cleavage rate when returned to normal sea water and fertilized. The developing larvae ranged from forms showing considerable inhibition (increased mesenchyme, shortened anal arms, undifferentiated oral lobe) to larvae (approximately 35%) which consisted entirely of ectoderm and ectodermal structures. These ectodermized forms were modifications in the same direction as the ‘animalized’ forms produced in the sea urchin by Lindahl 1 and Hörstadius 2 with NaCNS treatment and experimental isolation of animal blastomeres. Neither mesenchyme, pigment nor gut was present. With higher concentrations or exposure periods the number of ectodermized forms was decreased and the number of inhibited forms increased. When NaCNS was used in normal sea water only inhibited larvae resulted. Ca-free sea water alone had little effect.

Fertilized eggs treated with NaCNS (20-30 cc .54 M NaCNS plus 100 cc normal sea water) for 12-24 hours appeared as thick-walled radially symmetrical blastulae usually containing a surplus of mesenchyme and showing a loss of cells from the vegetal region. When these forms were returned to normal sea water as many as 95% developed into exogastrulae with large evaginated entoderms, often filled with mesenchyme, and with ectoderm reduced to a small pig-mented knob. Such forms were almost entirely entodermized and have been obtained by other workers (Herbst, 3 Child, 4 Horstadius, 2 etc.) with various methods in this and other forms.