THE CRUSTACEA 125 



It may be found by turning over stones under which 

 there is decaying sea-weed, and it seems to revel in these 

 malodorous conditions, conditions that would be speedily 

 fatal to any other of the denizens of the sea. 



It swims awkwardly, and yet rapidly, on its side. 



The Macrura (" Long-tailed " crustaceans). In the 

 preceding two true divisions of the Crustacea viz. the 

 Ampkipoda and Isopoda it will be seen, on looking at a 

 specimen (or at Fig. 48), that the body is pretty uniformly 

 divided into a number of segments, from head to tail, 

 and that there is no " fusion " or joining of any of these to 

 form what is known as the dorsal shield or carapace, (The 

 carapace-looking structure in the Leptostracan (Nebalia) 

 is of different origin, and the segmentation is within it.) 

 But in the Macrura we have the fusion of the majority 

 of the segments (on their dorsal side) to form the carapace. 

 As a rule fourteen segments are so joined, and six are free 

 to form the flexible abdomen and tail, while each segment, 

 fused or free, bears two pairs of appendages, legs, or their 

 modifications, antennae, eyes, foot- jaws, etc. 



The young emerge from the egg in a form not/quite 

 like the parent, and have to undergo a change or two before 

 the adult form is reached. 



The Macrura are divided into a number of sub-divisions 

 and families Astacidce, the lobsters : Palcemonidce, the 

 prawns ; Crangonidce, the shrimps, etc. which we will not 

 trouble about at present, but take the most familiar ex- 

 amples first. 



Homarus vulgaris, the common lobster (Fig. 49). This 

 is abundant on all our shores. A full-grown male measures 

 about fifteen inches from rostrum to tail. The female is 

 rather shorter, and broader in the segmented part i.e. the 

 abdomen. 



The young, on quitting the egg, are nearly of the form of 

 the parent. They escape from the eggs while these are still 



