172 ARTHKOPODA 



PORCELXIO 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 decaying 

 vegetable matter. To what class of the Arthropoda do they be- 

 long? 



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 present, the first pair being 

 rudimentary. 



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

 dihles, two pairs of maxillos, and one pair of 7naxillipeds. 



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



(e) Notice the character and number of the abdominal appen- 

 dages. 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. 



These animals are very common on hydroids, but because of 

 their peculiar shape and slow motions are rather inconspicuous. 

 Watch the animals and see how they move. Is the body kept 

 at rest and moved by the action of the appendages, 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 modification 

 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 num- 

 ber and shape in male and female? The first represents the head 



