RESPIRATORY ORGANS IN DEOAPODOUS CRUSTACEA. 451 
On the Ancestral Development of the Respira- 
tory Organs in the Decapodous Crustacea. 
By 
Florence Buchanan, 
(A Paper read to the Biological Society of University College, London.) 
With Plate XL. 
In the Crayfish, so well known to all students of zoology, 
our attention is attracted to the varying positions of the gills, 
and, in reading Professor Huxley's book, especially devoted to 
this Crustacean, we are led to compare the different positions 
of these organs and their relations to each other in the dif- 
ferent segments in many of the Decapods. In so doing the 
question arises as to how they have come to be situated as 
they are, and it is to this question that I propose, in the 
following paper, to attempt an answer. It must, I am afraid, 
be only a suggestion as to the real answer, since several details 
in the development of the various forms would have to be care- 
fully worked out in order to prove the whole theory true. 
For a great many of the ideas and facts cited I am indebted 
to a paper by Professor Claus in the ‘ Wiener Arbeiten * for 
1886. Other facts I have derived from the account by Professor 
Sars of the Schizopods brought up in the “ Challenger ” expe- 
dition. (The figures also are mostly from both these sources.) 
In order to explain the present positions of the branchiae 
of such forms as Astacus, it is needful first to find out what 
their past positions were, and for this we look not only to the 
early history of the individual, but also to the early history of 
the race. 
The Chaetopod-like ancestor of the Crustacea probably had 
