GENERAL BIOLOGY 



III. DIGESTIVE TRACT. 



(a) Carefully remove the anterior part of the carapace and 

 notice the very large sac-like stomach anterior to the heart. Pass a 

 probe into it through the mouth and short oesophagus, (b) Dis- 

 sect away the exoskeleton and muscles and follow the intestine 

 from the stomach to the anus. Immediately posterior to the stom- 

 ach is the "mid gut" having a short dorsal diverticulum on it. 

 The remainder of the intestine is the "hind gut." (c) The digestive 

 gland (the so-called "liver") forms a yellow mass opening by a 

 duct on each side of the mid gut. Wash away its contents if the 

 duct cannot otherwise be found, (d) Remove the stomach and 

 cut it open along one side (under water) and note a large round 

 (cardiac), and a narrow posterior (pyloric) portion. The chitinous 

 lining forms in the cardiac portion three conspicuous tooth-like 

 thickenings, the so-called "gastric mill." In the pyloric region 

 ridges, set with hairs, reduce the lumen of the stomach to a nar- 

 row slit. 



IV. EXCRETORY ORGANS. 



1. Green Glands. 



In front of the stomach is a pair of sac-like structures, the 

 green glands, or nephridia; each consists of a ventral glandular 

 part and a dorsal saccular portion, the latter opens to the exterior 

 by a duct. 



2. External Openings. 



On the basal joint of each antenna observe a papilla with the 

 external opening of the green gland at its summit. 



Draw a side mew of the digestive tract and excretory organs. 



IV. NERVOUS SYSTEM. 



Remove the muscles of the abdomen until the nerve cord is seen 

 along the ventral wall of the body, (a) Note the relation of the 

 ganglionic swellings to the somites, (b) Follow the cord into the 

 thorax; here it enters a canal, the roof of which must be broken 

 off bit by bit with forceps to show the nerve cord. Note the 

 number of ganglia in the thorax, (c) The cord divides at the 

 oesphagus into a right and left half which meet again at the 

 brain. The brain, or supraoesophageal ganglion, lies just posterior 

 to the eye stalks, close to the exoskeleton, and sends a large nerve 

 into each of the eye stalks. 



Make a drawing of the nervous system. 



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