184 ARTHROPODA 



PORCELLIO OR ONISCUS (Sow-bug) 



These animals occur in damp places, such as under stones, 

 logs, etc., and in cellars. They live for the most part on de- 

 caying vegetable matter. To what class of the Arthropoda 

 do they belong? 



1. Notice the shape. Is this an adaptation? 



2. Is the body divisible into head, thorax, and abdomen? 

 Count the number of segments. Is there any evidence of 

 fusion at the posterior end of the body? 



3. Examine the appendages. 



(a) Are the eyes stalked or sessile? 



(6) Only one pair of antennae is well developed, the first 

 pair being rudimentary. 



(c) The mouth appendages are small. They consist of 

 mandibles, two pairs of maxillae, and one pair of maxillipeds. 



(d) How many walking legs are there? Are these all 

 alike? 



(e) Notice the character and number of the abdominal 

 appendages. On the posterior surface of all but the last pair, 

 which are modified to form anal feelers, are gills. These are 

 the only respiratory organs. Why must these animals live 

 in damp places? 



Make a drawing of the animal from the ventral side. 



CAPRELLA (Goat Shrimp) 



These animals are very common on hydroids, but because 

 of their peculiar shape and slow motions are rather incon- 

 spicuous. Watch the animals and see how they move. Is 

 the body kept at rest and moved by the action of the ap- 

 pendages, or how is movement from place to place effected? 

 Are the appendages adapted for grasping? Watch specimens 

 and see if you can determine on what they feed. 



The form is of interest because of its extreme modifica- 

 tion to suit it to the needs of its life. There is some difference 

 in the structure of the male and female. 



1. Count the segments of the body. Do they differ in 



