37 



VIII. — On the Structure of the Fldbella of some of the higher forms 

 of Crustacea, with some remarks on their probable use in the 

 function of respiration. By John Quekett, Esq., Assistant 

 Conservator of the Museum of the Royal College of Surgeons of 

 England. 



(Read May 21, 1845). 



The respiratory organs of the Crustacea are with the common con- 

 sent of authors called branchice, a term which applies equally to those 

 which live on land as well as to those which inhabit the water. 



In some members of the class, the branchial organs are very com- 

 plicated, and consist of an apparatus designed especially for the de- 

 carbonization of the blood, in the shape of quadrangular pyramids, on 

 whose sides are disposed parallel lamellae, or tubes, on which the res- 

 piratory vessels are distributed. These organs are contained in an 

 especial cavity, and further provided with an apparatus for the pur- 

 pose of causing fresh currents of water to pass over the extended res- 

 piratory membranes. In other Crustacea no branchiae are present, 

 and the function of respiration is performed by certain appendages 

 either to the locomotive or digestive system, which do not exist for 

 the office exclusively, but are modified in such a particular manner 

 as to perform the all-important function of respiration. 



From the researches of Dr. Milne Edwards, it would appear that 

 the embryo of the common cray-fish, Astacus Jluviatilis, presents 

 four principal periods in the development of its respiratory apparatus. 

 Istly. — That which precedes the appearance of branchiae. 2ndly. — 

 That during which the branchiae are not distinguishable from the fla- 

 belliform appendages of the extremities, and which appear as mere 

 processes of other organs destined either for locomotion or mastica- 

 tion. 3rdly. — The transformation of these organs into others of a 

 more complex nature, but still external. And lastly, that during which 

 the branchiae sink inwards and become lodged in a cavity especially 

 adapted for their reception, and provided with a particular apparatus 

 destined to renew the water necessary to the maintenance of respi- 

 ration. 



The first of these conditions is presented to us in some of the infe- 

 rior Crustacea which have no special apparatus for respiration ; the 



