A CYTOCHEMICAL INVESTIGATION OF OÖGENESIS AND DEVELOPMENT TO THE SWIMMING LARVAL STAGE IN THE CHITON, CHITON TUBERCULATUM L

¹ Bermuda Biological Station, St. George's West, Bermuda, and Department of Biology, Johns Hopkins University, Baltimore, Md.

1. Oöcyte growth and development and the subsequent development of the egg to the swimming larva stage were investigated in the chiton, Chiton tuberculatum, using topological cytochemical methods for nucleic acids, proteins and mucopolysaccharides.

2. The growing oöcytes exhibited two phases of synthetic activity: the first phase was chiefly concerned with RNA production and the second phase with protein yolk synthesis.

3. A probable alteration in the cytoplasmic RNA-protein complex prior to the initiation of yolk synthesis was detected by an alteration of the affinity of RNA-associated proteins for binding acid dyes in mixtures.

4. Oöcyte accessory cells were probably responsible in some way for chorion formation. After the chorion was formed, ornate hollow processes grew out of the chorion, each beneath an accessory cell. When development of the processes was completed, the accessory cells had disappeared.

5. There was no evidence of new synthesis of RNA in any of the cells of the developing embryo except the cells of the prototroch and apical tuft. This applies to the complete developmental history of the oöcyte from the cessation of RNA synthesis prior to protein yolk formation in the oöcyte to the swimming trochophore larva.

6. Since primary differentiation occurs in mosaic embryos in the absence of synthesis of new RNA, the possibility that primary differentiation is controlled by the RNA produced in the oöcyte was discussed.

7. Although there was no differential segregation of protein yolk into the blastomeres—both RNA-basophilia and protein yolk being evenly distributed in all blastomeres—the posterior blastomeres received a larger proportion of yolk material than the micromeres. This was particularly evident in the yolk-laden cells of the trochophore gut.