592 BIOLOGY. 



Eighth Class. 



Branchial, Pedal Animals Crustacea. 

 Conchozooid Ancyliozoa. 



3507. The Crustacea are Worms with horny rings to 

 the body, jointed feet and tentacula, which mostly breathe 

 by branchiae. 



They correspond to the Conchozoa, or Shell-animals, 

 and divide therefore into three orders, each of these 

 including six families. 



Here belong the Crabs, Wood-lice, and Spiders. 



In the lowest forms the head, thorax, and abdomen 

 are blended together, and the back mostly covered with 

 a great horny scute Mussel-like Insecta. 



In the next place the thorax and abdomen admit of 

 being clearly distinguished, both by their form as well 

 as by their appendages, which are much larger on the 

 thorax, as in the Cray- fish. 



Then follow cylindrical forms with numerous feet, 

 appended to uniform rings, but having a head free and 

 distinguished by tentacula, maxillae, and eyes Wood-lice. 



The Wood-lice bear a resemblance to the air-breathing 

 Insects, although all parts of the body still pass over or 

 blend gradually into each other. 



In the Arachnida or Spiders aerial respiration takes 

 place, and their body enters into relations with the 

 more highly organized Insects, since the head becomes 

 small, the abdomen large, thick, and short. 



As the Crustacea pass parallel to the Conchozoa or 

 Shell-animals, so do they divide into three cohorts or 

 groups : the Mussel-, Snail-, and Kracken-like Crus- 

 tacea, or Crabs, Wood-lice, and Spiders. 



COHORT I. MUSSEL-LIKE CRUSTACEA CRABS. 



3508. Head and thorax connate, being mostly covered 

 with a shell or shield, abdomen stunted or caudiform ; 

 maxillae and branchiae present. 



Order 1. Lochmuschelartige, Pfriemenkrebse. 



3509. The feet mostly simple and pointed, without 



