SQUILL A. 165 



(e) The abdominal appendages. Are they all alike? What 

 functions are performed by them? 

 Make a drawing. 



SQUILLA. 



Compare the animal carefully with the lobster, noting all of 

 the important differences. The posterior three thoracic seg- 

 ments are free. The male possesses a copulatory organ on the 

 basal joint of the last thoracic leg. In the female the opening of 

 the oviducts is in the mid-ventral line, on the next to the last 

 thoracic segment. Examine the chelae 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 be 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. 



