vill PREFACE. 
unnecessary to burden the text; and, under the 
head of Bibliography, I have given some references 
to the literature of the subject which may be useful 
to those who wish to follow it out more fully. 
I am indebted to Mr. T. J. Parker, demonstrator 
of my biological class, for several anatomical draw- 
ings; and for valuable aid in supervising the 
execution of the woodcuts, and in seeing the work 
through the press. 
Mr. Cooper has had charge of the illustrations, 
and I am indebted to him and to Mr. Coombs, 
the accurate and skilful draughtsman to whom 
the more difficult subjects were entrusted, for 
such excellent specimens of xylographic art as 
the figures of the Crab, Lobster, Rock Lobster, 
and Norway Lobster. 
dy de Jel 
Lonpon, 
November, 1879. 
