146 ARTHROPODA. 



1. Postero-laterally are two firm prominences, the flanks, 

 containing muscles. What are these muscles for? Anterior to 

 these are the gill chambers covered by a thin cuticle. Remove 

 this and note the gills with their tips converging medially. 



2. Between the gill chambers and flanks is the delicate peri- 

 cardium. Remove this and find the heart with its ostia. An- 

 teriorly it sends out an ophthalmic artery and two antennary 

 arteries. Just anterior to the heart are muscles which were 

 attached to the shell. What organs do they supply? The an- 

 tennary arteries pass through the heads of a pair of the muscles. 



3. In front of the gill chambers are the gonads. In the female 

 the orange ovary will be seen lying on the yellow liver. In the 

 male the slender, wavy, white cord, the testis, lies in approxi- 

 mately the same position. 



4. The heart is attached to the pericardium by muscular 

 strands. Cut these, and the three anterior arteries, and remove 

 the heart, noting the two hepatic arteries beneath the antennary 

 arteries, the great sternal artery passing downward from the 

 under side, and the small abdominal artery just behind the last. 



Draw dorsal and ventral views of the heart to show the ostia 

 and the origins of arteries. 



5. Cut across a gill and notice its afferent and efferent vessels. 

 The latter is continuous with one of the sinuses which empty 

 into the pericardial cavity. Can you determine how many 

 sinuses there are ? Do you understand how the heart receives 

 blood? 



Reproductive System. Beginning antero-laterally, on one 

 side, dissect out the reproductive organs, noting at the same time 

 the distribution of arteries. 



(a) Female reproductive organs. Each ovary passes inward 

 and backward, anastomoses with the one of the other side be- 

 hind the stomach, and extends back to the abdomen. On a 

 level with the posterior part of the stomach a branch passes down- 

 ward and outward and is continuous with a dense, white organ, 

 the seminal receptacle. Leave this receptacle in place but remove 

 the entire ovary. 



