140 ARTHROPODA. 



the oviducts is in the mid-ventral line, on the antepenultimate 

 thoracic segment. Examine the chelse and compare them with 

 the chelse of a lobster. Are they homologous appendages in the 

 two animals? If you have living specimens, study their move- 

 ments while walking and swimming. 



A drawing of a side or ventral view will he profitable. 



Internal Anatomy. — 1. Remove the top of the carapace and 

 abdomen. Beneath the muscles note the elongated, white tube, 

 the heart, which extends from the stomach to the fifth abdomi- 

 nal segment. The anterior end is slightly enlarged and gives 

 rise to the anterior aorta. The posterior end gives rise to a 

 posterior aorta. Note lateral arteries and ostia. Remove the 

 heart. 



2. Beneath the heart, in the male, is a whitish, pigmented, 

 flattened mass which consists of two convoluted tubes, the testes. 

 Cut this mass across between the second and third abdominal 

 segments and force it posteriorly. The two testes are continu- 

 ous posteriorly. Follow them anteriorly and find the slender, 

 dense, coiled vasa deferentia passing outward and downward 

 at the posterior end of the third thoracic segment. Cut them and 

 lay them back where they can be dissected later. The testes ex- 

 tend forward to the region of the stomach. Remove the testes. 



3. Beneath the heart, in the female, are the two ovaries. 

 Trace them forward and backward, and find the very slender 

 oviduct that extends from each outward and downward in the 

 region of the antepenultimate thoracic segment. Remove the 

 ovaries, deferring the tracing of the oviduct. 



4. Beneath the reproductive organs, in both sexes, is the 

 granular liver. This consists of two lobes which extend from the 

 stomach to the end of the telson. They form saccular diverticula 

 between segments and in the telson. Where do they open into 

 the alimentary tract? 



5. Free the intestine, which is between the lobes of the liver. 

 The rectum is in the sixth abdominal segment. 



6. Pull back the anterior end of the stomach, identify the 

 circum-esophageal connectives, in order not to destroy them, 



