272 



ZOOLOGY 



Crustacean characters than their parasitic congeners, but owing 

 to their fixed habit of life they have undergone numerous 

 modifications. Both the parasitic and sessile forms pass through 

 a freely mobile larval stage, and it is not until they reach 

 the last of numerous larval stages that they either attach 

 themselves to some host or settle down upon some foreign 

 body. Whilst this is taking place, the larva, which is now in 

 what is termed the Gypris stage, takes no food, but lives upon 

 the nutrient material stored up in a well-developed fat-body, a 

 condition of quiescence which recalls the pupa stage of many 

 insects. 



Like so many other sessile animals, the Thoracica fix them- 

 selves by their head ; the anterior end of this in the Lepadidae 



Fig. 161. — Side view of Lepas anatifera. 

 After Leuckart. 



1. Stalk. 



2. Carina. 



3. Tergum. 



4. Scutum. 



grows out into a long stalk which projects beyond the shell, 

 and serves to lodge some of the internal organs of the body. 

 The body is enclosed in a reduplication of the skin, which is 



