204 



ARTHROPODA 



cements the legs together in masses which are carried on the 

 " ovigerous " legs of the male, and in one species on the female. 

 The nervous system consists of cerebral, subesophageal and three 

 other thoracic ganglia with two pairs of abdominal ganglia. Meta- 

 morphosis usually occurs. The larvae of one genus are parasitic 

 on the Coelenterata. They have no economic significance. 



Fig. 96. Limiilus polyphemus, the king-crab. A, dorsal view. /, carapace; 2, 

 meso- and meta-soma; j, telson; 4, median eye; 5, lateral eye. B, ventral view. 

 /, carapace; 2, meso- and meta-soma; j, telson; 4, chelicera; 5, pedipalp; 6, 7, 8, g, 

 3d to 6th appendages, walking legs; 10, genital operculum turned forward to show 

 genital aperture; //, 12, /j, 14, IS-, appendages bearing gill books; 16, anus; //, mouth; 

 /<?, chilaria. (From Shipley and McBride. Courtesy of Macmillan and Co., Ltd.) 



Tardigrada. — The Tardigrada, slow-moving forms called " water 

 bears " are small soft-skinned animals living in fresh and salt 

 water or damp moss. They have four pairs of short-hooked, un- 

 jointed legs. The digestive tract is well developed, the buccal cavity' 

 containing teeth sometimes calcified. Their muscles are non- 

 striated. No respiratory or circulatory organs are developed. The 

 gonads are saccular and empty into the rectum. The nervous 

 system consists of cerebral ganglia, and a nerve cord with four 

 ventral ganglia. 



General Consideration of the Arthropoda 



Chaxacteristics and Distribution. — Deep sea Crustacea are huge 

 in size and have a brilliant red coloring. Some are phosphorescent. 



