TRANSCRIBER'S NOTE:
Raised dots in numbers were converted to decimals.
Use of periods and commas in the abbreviations within and referring to figures and plates is inconsistent. Often, punctuation marks do not match the illustrations to which they refer. Periods were retained; commas were added to separate figure numbers from abbreviations within the figure. Spacing within the abbreviations was standardized.
Footnotes were renumbered sequentially, and were moved to the end of the plate explanation.
Changes for consistency within the text of the book:
body cavity to body-cavity
body wall to body-wall
choroid-slit to choroid slit