THE DECAPOD CRUSTACEA. 155 



Notice, first, that the shield, or carapace, is prolonged 

 forward between the eyes into the strong spiny beak, that 

 in its anterior region it has a strongly marked groove which 

 runs forwards to end near the outer side of the second pair 

 of antennae, or feelers, and that it is prolonged at either 

 side into the large gill-covers which protect the lateral gills. 

 Besides the distinct groove, other dorsal markings divide 

 the carapace more or less distinctly into regions. Of these, 

 the most distinct are the gastric region immediately behind 

 the rostrum, with a hepatic region at either side. Behind it 

 is the cardiac region, which has at either side the large 

 branchial regions. The regions are named after the organs 

 which lie beneath them, and are indicated in the figure of 

 the crab. The tail differs considerably from the anterior 

 part of the body, for it consists of six similar rings, each 

 carrying a pair of appendages, and an end piece, or telson, 

 without appendages. Each ring consists of an arched 

 dorsal portion, two projecting side flaps, a socket for the 

 limb, and a ventral bar with a spine in the middle. 

 Typically in the Crustacea the whole body should consist 

 of such rings, but in the three specimens chosen the 

 anterior thirteen rings are fused together, and are over- 

 lapped by the great shield, which has grown backwards 

 from the anterior segments. The function of this shield, 

 as already seen, is to protect the viscera and gills. 



Perhaps at this point it may be well to interpolate a note 

 on terminology. To the beginner it may seem that the 

 greatest drawback to the study of Natural History is the 

 number of technical terms used to describe even the simplest 

 animal, and that the number of these terms has been need- 

 lessly multiplied. This last is perhaps a point which might 

 be debated, but we may notice that the use of technical 

 terms is justified on two grounds. First, they have perfectly 

 definite meanings, which cannot be said of the majority of 

 their Anglo-Saxon equivalents; and, second, they express 

 concisely, and in a word, a meaning which it would require 

 an English phrase to make clear. The term Decapod 

 Crustacea, for example, gives a naturalist a perfectly clear 

 idea of a group of animals which would in English be 

 inadequately described as "hard-coated animals with ten 

 legs." Although, therefore, an effort has been made to 



