136 ARTHROPODA. 



understood; first maxilla, thin and leaf-like; mandible with two 

 hard rods for the attachment of muscles. 



10. Detach and examine one each of the eyes, antennules, and 

 antenna. On the flattest side of the basal joint of the anten- 

 nule note a dark suture the scar of the former opening into the 

 otocyst. Do you understand what function is performed by the 

 otocysts? Near the base of the antenna find the opening of the 

 renal organ (green gland). 



11. Compare each of the five walking legs (pereiopods) with 

 the third maxilliped. Which part, endopod or exopod, is lack- 

 ing? Which bear forceps or chelae? Why is this so? Note in 

 the male the openings of the sperm ducts on the coxopods of the 

 fifth pair. 



Internal Anatomy. Remove the entire dorsal part of the 

 carapace. 



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 antcnnary 

 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. 



