Obvious typographical errors have been corrected. Original published spelling and hyphenation have been retained as they appear in the original publication, including "debateable" and "cellless". A possible missing "wall" has not been added to the caption for Fig. 5 ("--muscular of intestine"; and reference to "the Italian poet" on Page 138 of the original publication has been preserved. Where figures or tables cut paragraphs, they were moved above or below the paragraph.