102 THE FRESH- WATER CRAYFISH— THE CAPE CRAWFISH 



endopodite is very small, and the exopodite is fused with the epi- 

 podite to form the scaphognathite or baler. The function of the baler 

 is respiratory ; it causes a constant forward current of water in the gill 

 chamber. [In Jasus the protopodiie has three pointed prolongations 

 and is very small.] 



(b) The first maxilla consists of three leaf-like parts, the basal two being 

 the protopodite, while the single distal one is the endopodite. The 

 exopodite is absent. 



■(c) The mandible consists of a strong and transversely elongated proto- 

 podite, bearing a three-jointed palp, which is the endopodite. [In 

 J asm the based joint of the palp is regarded as the protopodite, and the 

 remaining joints as the endopodite.] 



(d) The antenna has a two-jointed protopodite. The basal joint is small, 



and on its ventral face is the opening of the " green gland." The upper 

 joint is larger and externally it bears a broad flat exopodite or squame, 

 while internally the feeler, the elongated endopodite, is attached to it 

 by two stout basal joints. [In Jasiis there is no exopodite, and the 

 basal joint of the protopodite is fused to the body.] 



(e) The antennule has a three-jointed base (the protopodite) and two 



terminal flagella representing the exopodite and the endopodite. [In 

 Jasus the protopodite is two-jointed, the endopodite is a single two-jointed 

 rod terminating in two small flagella, and the exopodite is absent] 



Draw the above appendages. 



Second Day 

 Internal Structure. 



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

 from behind forwards and remove the branchiostegites of each side. Carefully 

 raise the central part of the carapace from behind, separate it from the under- 

 lying integument, and then remove it completely by severing it just behind the 

 rostrum. Cut through the tergal or dorsal portions of the abdominal segments 

 on both sides and remove them. Remove the brightly pigmented tissue which 

 lines the inside of the carapace, so as to expose the internal organs. 



Note the following structures : — 



(a) The dorsal extensor muscles, paired longitudinal bands along the dorsal 



region of the abdomen and inserted into the front of each segment. 



(b) The large abdominal flexor muscles, occupying the ventral region of the 



abdomen, and arising from the endophragmal skeleton. 



(c) The dorsal extensor muscles, arising from the sides of the thorax. 



(d) The " stomach " or gizzard, situated in the anterior region of the 



cephalo-thorax. Notice the two pairs of muscles, arising from the 

 body-wall, which work the gizzard. 



(e) The adductor muscles, working the mandibles, situated on either side of 



the posterior end of the gizzard. 



