LOBSTEE OE CEAYFISH 143 



groove. That part of the carapace lying between 

 them covers the heart. Examine the frontal 

 spine or rostrum projecting from the carapace. 

 What is its shape ? Size ? Structure ? Color ? 

 How fastened to the carapace ? Is it movable ? 

 Is it an appendage ? Compare the rostra of sev- 

 eral specimens. Turn the animal over on its back. 

 What traces of segments do you find on the ven- 

 tral side of the cephalothorax ? Are the segments, 

 movable ? Note the shape of the sterna of these 

 segments. Examine the margin of the carapace. 

 Does the shape of the margin bear any relation to 

 the number of legs? With a pair of forceps or the 

 handle of a scalpel raise up this margin, and note 

 that a part of it, the branchiostegite, extending 

 downward from the branchio-cardiac groove, is 

 free from the body. Is this portion comparable to a 

 single pleuron or to several fused together ? Why ? 

 With a pair of strong scissors cut the branchio- 

 stegite away on one side, and note the structure of 

 the skin lining the inner surface of the branchio- 

 stegite. What outgrowths does the skin bear? 

 ISTote all the differences between the outer and 

 inner surface of the branchiostegite. ISTote the 

 cavity, the gill-cavity or branchial chamber, 

 covered by the branchiostegite. With a pair of 

 strong scissors make a transverse section of the 

 cephalothorax just behind the large claws. Care- 

 fully pick away the soft parts, or clean thoroughly 

 by boiling for five to ten minutes in caustic potash, 

 and compare with the third abdominal segment. 

 What differences in the shape of the tergum ? Note 

 on it the two small prominences or endotergites 

 near the middle. In what way is the sternum 



