52 INVERTEBRATE ZOOLOGY 
a relatively much larger cephalothorax and abdominal append- 
ages, and is much more crab-like than the zoéa. 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 zoéa, 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 larve in the mysis stage and study them 
under the microscope. The lobster is born in a more advanced 
condition than is the crab. The zoéa 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. 
