CRUSTACEA 130 



Scutigera forceps is a common centiped seen running 

 about in dark cellars or basements. It is entirely harmless. 

 Other harmless centipeds are found under logs and stones. 

 Scokpendra is the genus of the poisonous centipeds of 

 the South, the West Indies, and South America. They 

 are from six to ten inches long, and with their poison fangs 

 are capable of inflict- 

 ing serious bites on 

 man. 



The galley worm 

 (Spirobolus), a com- 

 mon species of mille- Fm 154< _ Galley worm . 



ped, lives under 



stones and logs where it feeds on dead snails and earth- 

 worms. Polydesmus is a flat milleped found in moist 

 places. 



9. CRUSTACEA 



The crustaceans differ from the other arthropods in 

 usually breathing by gills and having two pairs of antenna. 

 Many forms possess a hard outer skin or exoskeleton to 

 which the name of the class is due. The fresh water cray- 

 fish (Cambarus) and the lobster (Homarus) are so similar 

 in structure that a description of one applies almost equally 

 well to the other. 



The body of the crayfish, bearing nineteen pairs of appen- 

 dages, is divided into a cephalothorax and abdomen. The 

 former, including the head and thorax, is covered by a cal- 

 careous shield, the carapace, which when broken off on the 

 sides reveals the gills composed of feathery filaments with 



