ERRATA 
Page 44, line 1 of text, for ‘“sludge-worms” read midge larvae, and for “larvae 
of the midges” read sludge-worms. 
Page 188, line 4, for 3 read 23. 
Page 216, last line, for “the opposite page” read page 214. 
Page 267, delete line 13 from bottom. 
Page 382, lines 3 and 5 from bottom, for “decrease” read change. 
