152 ARTHROPODA. 



PHOXICHILIDIUM. 



The exact affinities of the pygnogonids to other forms is 

 not known, but they have certain characters that have suggested 

 a possible relationship to the Arachnoidea. They are frequently 

 found in considerable abundance on the material that is attached 

 to piles. Notice their movements and see how they cling to the 

 material on which they are moving. 



1. The body is very slender and is composed of a number of 

 free segments that form the head and thorax and a small, ves- 

 tigial abdomen. How many free segments are there? At the 

 anterior end is a rather prominent proboscis, with the mouth at 

 its end. 



2. The following appendages will be found: 



(a) The chelicerce. What is their structure? Are they 

 armed with pincers? 



(6) Four pairs of long walking legs. How many segments 

 have they? The viscera extends into the bases of these appen- 

 dages. 



(c) The male is provided with a pair of ventral appendages 

 called the ovigerous legs, by means of which the eggs are collected 

 as they are laid by the female. These appendages are not present 

 in the female. 



Make a drawing of the under side of a specimen. 



MYRIAPODA. 



LITHOBIUS. (Centipede, Earwig.) 



These animals may frequently be found under stones, logs 

 or boards, or about rubbish or manure heaps. They live largely 

 on insects, larvae, and small worms, and are very active. 



1. Notice the shape of the body and count the number of 

 segments. Is there a distinct head? Arc the segments very 

 movable ? 



2. How many appendages docs each segment possess? Are 

 all of the segments provided with appendages? Allow the ani- 



