GENERAL BIOLOGY 



Compare your drawings of the different kinds of appendages, 

 labelling homologous parts with the same name; the 19 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. CIRCULATORY SYSTEM. 



1. Heart. 



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

 the pericardial sinus, within which lies the polygonal, flat 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. 



2. Arteries. 



Running anteriorly from the heart are : (a) the opthalmic artery 

 in the mid-line and lateral to this, (b) a pair of antennary arteries, 

 (c) a pair of hepatic arteries; posterior to the heart are: (d) the 

 median abdominal artery from which (e) the sternal artery runs 

 to the ventral side just posterior to the heart. 



Draw the heart and arteries. 



II. REPRODUCTIVE ORGANS. 



Carefully remove the heart to expose the reproductive organs. 



(a) 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 thorac 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 the same 

 general form and position as the testes in the male, (d) Oviducts. 

 These are short and go directly down from the ovary to the open- 

 ings on the third, or middle, ambulatory appendages. 



Make a drawing of your dissection, showing all these organs in 

 place. 



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