the protoplasm has been transformed into the contractile substance of the flagellum.
I have not been able to measure the volume of muscle cells in Crepidula, but such measurements have been made by Eycleshymer[1] for the striated muscle cells of Necturus. From the measurements given by Eycleshymer, I have calculated the nucleus-plasma ratio in the usual manner, i. e., by determining the ratio of the nuclear volume to the cell volume less the nuclear volume; and I find that in the 7 mm. and 8 mm. embryos this ratio is about 1 :11, whereas in the 23 cm. adult it is about 1 :73. The increase of cell substance is therefore less than seven times, instead of twenty or thirty times, that of the nucleus, as he states.
Ratio of Nuclear Volume to Cell Volume in Adult Individuals of Crepidula plana[2]
It is important to note that Eycleshymer found that as the fibrillæ are progressively formed out of the protoplasm of the cell, the nuclei are crowded out of the center of the cell toward its periphery; that the nuclei become more densely chromatic, and especially so on the side of the nucleus toward the fibrillæ; and that possibly the nuclei may disintegrate and their chromatin go to form the dark bands of the striated
