III. CEPHALIC APPENDAGES. 



These are the maxillae, mandibles and antennae. 



(a ) Second or post maxillae; the endopodite is not jointed, while 

 the two parts of the protopodite are subdivided or cleft ; the large 

 oval plate, seaphognathite, acting to bail water out of the branchial 

 chamber, represents the epipodite and probably also the exopodite. 

 (b) First maxilla ; this is very small and lies close to the mandible. 

 It is divided into three parts representing the coxopodite, basipodite 

 and endopodite. ( c ) Mandibles ; each has a strong basal part 

 bearing a two jointed palp or endopodite. ( d ) Post antenna ( antenna 

 proper); each has a two jointed protopodite with the opening of 

 the green glands on a tubercle on the proximal joint, the scale-like 

 plate is the exopodite and the long, filiform, many jointed part is 

 the endopodite. (e) First antenna (antennula); here the pro- 

 topodite has three joints and bears a long many jointed endopodite, 

 and a similar exopodite, while upon its large proximal joint is the 

 opening of the auditory organ, surrounded by hairs. 



Compare your drawings of the different kinds of appendages, 

 labelling similar parts with the same name: the IQ pairs may be 

 regarded as modifications of such a one as the third maxillipede. 



E. INTERNAL ORGANS. 



Pin the crayfish down under water, dorsal side up, and carefully 

 remove the carapace bit by bit with strong forceps, commencing at 

 the free posterior border. 



I. HEART. 



Posterior to the cervical suture, a median chamber is laid bare, 

 the pericardia! sinus, within which lies the polygonal, fiat heart 

 which has six openings into the pericardinal sinus, two on the 

 dorsal surface, two on the lateral surfaces, and two on the ventral 

 surface. 



II. REPRODUCTIVE ORGANS. 



Carefully remove the heart to expose the reproductive organs. 

 fa) Testes ; in the male, these form a Y-shaped mass with the 

 smallest of the three lobes passing back along the median line. 



(b) Vas deferens. Cut away the thoracic wall on one side and 

 trace the much convoluted tube from the union of the posterior 

 and anterior lobes of the testes down to the external genital 

 opening on the posterior ambulatory appendage on that side. 



(c) Ovary. In a female specimen the larger reddish ovaries have 



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