MORPHOLOGICAL EFFECTS OF COBALTOUS CHLORIDE ON THE DEVELOPMENT OF LIMNAEA STAGNALIS AND LIMNAEA PALUSTRIS

Abstract

1. The effect of cobaltous chloride (CoCl2) on the developmental stages of Limnaea stagnalis and L. palustris has been studied.2. Eggs and embryos were treated for 24 hours with various concentrations of CoCl2. Effective concentrations of CoCI2 ranged from 1 x 10-5 to 1 x 10-4 M for L. stagnalis and from 2 x 106 to 8 x 10-5 for L. palustris.3. Variations in resistance to CoCl2 were observed between species at the same stage of development, between eggs treated at different stages of development and between eggs from the same egg masses treated at the same stage of development.4. Treatment with CoCl2 resulted in (a) separation of blastomeres, (b) vesicular and dumbbell-shaped exogastrulae, (c) arrested gastrulae, (d) veligers with a reduced larval liver, shell and foot, and with a fluid-filled body cavity containing few mesenchyme cells, (e) shell-less snails with a reduced larval liver and shell and (f) helmet-shelled snails with abnormally wide shell apertures.5. Manganese, cadmium and nickel produced malformations similar to those caused by cobalt. The sequence of effective concentrations was Mn < Co < Cd < Ni.6. Sections of normal and cobalt-treated embryos showed an inhibition of the differentiation and proliferation of mesenchyme cells of the body and foot and an inhibition of proliferation and enlargement of the endoderm cells of the larval liver.7. Exogastrulae and hydropic exogastrulae and veliger larvae appear to be caused by an impairment in the development of the mesomeres plus a concomitant uptake of water by the blastocoel or body cavity.8. Arrested veliger larvae and the differences in their development are explained on the basis of variation in the functional capacity of their larval livers.9. The morphological evidence indicates that the several characteristic malformations result from an inhibition of the cobalt-sensitive fourth quartette of micromeres and their derivatives, the mesomeres and larval liver cells.10. The results suggest that metal ion-reactive groups in the vegetal region of the Limnaea egg may be progressively segregated into the fourth quartette of micromeres.