94 THE FRESH- WATER CRAYFISH— THE CAPE CRAWFISH 



(e) The telson. 



(/) The anus, situated on the ventral surface of the telson. 



The Respiratory System. 



Cut along the branchio- cardiac groove of the left side with a pair of scissors, 

 and remove the branchiostegite so as to expose the branchial chamber with the 

 gills. The gills are soft and feathery vascular outgrowths. The stem of each 

 giU contains two longitudinal vessels (afferent and efferent), with which the 

 numerous hollow thin-walled filaments are connected. The gills receive differ 

 ent names according to their positions, and are thus divided into three sets : 



(a) The podobranchs, attached with the epipodites to the basal segment of 



each thoracic appendage except the first maxUlipedes and the fifth 

 walking legs. The epipodites are thin leaf-like plates directed up- 

 wards and Ijnng in the gill cavity between the thoracic wall and the 

 branchiostegite. 



(b) The arthrobranchs, attached to the membrane connecting the thoracic 



appendages with the trunk. They are usually in pairs, and are separ- 

 ated from the podobranchs by the epipodites. 



(c) The pleurobranchs, attached to the inner wall of the branchial chamber 



above the attachments of the appendages. 



The number and arrangement of the gills in Astacus is as follows : — 



ep, signifies an epipodite. 

 r, signifies a rudimentary gill. 

 The figures in brackets show the differences in the gill formula between Astacus and Jasm, which 

 has/oMJ- pleurobranchs. 



JV.B.— The Norway lobster (Nephrops) has five podobranchs and a rudiment (on second 

 maxilliped), eleven arthrobranchs, and four pleurobranchs. 



The Appendages. 



Remove the appendages from the left side of the animal, commencing with 

 the uropods and working forwards to the head. Lay them out in the order in 

 which they were removed : — 



A. The Five Abdominal Appendages of the Left Side. 



There are appendages on all the abdominal segments except the telson. \In. 

 Jasus there are no appendages on the first and the last segments. '\ 



