ARTHROPODA. 191 



The higher crastacea are highly organized, possess- 

 ing nearly as many different kinds of organs as can be 

 named in vertebrates, although of course differing in 

 their relative positions and arrangement. The lobster, 

 for example, possesses a highly developed, nervous 

 system, with complex eyes and ears, and a correspond- 

 ing degree of intelligence ; gills for breathing ; an 

 alimentary canal consisting of gullet, stomach, and 

 intestine, and. supplemented by a paired ferment- 

 producing gland called the liver; a paired excretory 

 organ, the green gland ; a complicated muscular 

 system; a vascular system and heart, containing 

 blood, with stellate, amoeboid, colourless corpuscles ; 

 and complicated reproductive organs. 



The higher forms of Crustacea are distinguished by 

 the extent to which successive segments are fused and 

 modified. The anterior segments, including the head, 

 form the cephalothorax (head and. breastplate). The 

 name of Thoracostracci (breastplate-shelled) has been 

 accordingly given to them ; the group is also called 

 Podophthalmata (foot-eyed), because they are further 

 characterized by having their eyes carried on stalks. 

 The higher forms are included in the order Decapoda, 

 of which the division Macrura (big-tails) includes the 

 Lobsters, Cray-fishes, Shrimps, and Prawns ; and the 

 division Brachyura (short-tails) > the Crabs, so called 

 because in the adult the tail is greatly reduced : its 

 segments are small, and are permanently tucked under 

 and applied to the under side of the thorax. The 

 Crabs and Lobsters have a larval form called a Zoea' 



