46 INVERTEBRATE ZOOLOGY 



a relatively much larger cephalothorax and abdominal append- 

 ages, and is much more crab-like than the zoea. But it still 

 has a long abdomen, and at the end of this is a swimming fin. 

 The megalopa is a swimming animal, like the adult lobster, 

 but it is gradually assuming the characters of the adult crab. 

 Its two anterior maxillipeds have lost their locomotory char- 

 acter, which they possessed in the zoea, and have assumed their 

 final form and function. Identify all the mouth-parts. 



Exercise 2. Draw a dorsal view of the animal, with the legs 

 extended, on a large scale. 



Mount several lobster larvae in the mysis stage and study them 

 under the microscope. The lobster is born in a more advanced 

 condition than is the crab. The zoea stage of the lobster is 

 passed over in the egg, and when the young animal emerges 

 from the egg it resembles Mysis, a schizopodous crustacean, 

 and hence is said to be in the mysis stage. The general form 

 of the animal does not differ much from that of the adult. 

 The abdomen bears no appendages. The cephalothorax is 

 very nearly like that of the adult and bears the same append- 

 ages. The third maxilliped, however, is a locomotory append- 

 age, as it is in Mysis, and with the five periopods is used for 

 swimming. Notice the biramous character of each periopod. 



Exercise 3. Draw a side view of the animal on a large scale. 



