158 LIFE BY THE SEASHORE. 



in part by the fusion of the ventral and lateral elements of 

 the thoracic segments, and in part by additional structures. 

 It will be recollected that the cephalothorax or anterior 

 region is as truly formed of segments as the abdomen, but 

 that it is overlapped by the great shield which has developed 

 from the anterior segments. In consequence, the skeleton 

 of the overlapped segments has in part disappeared, in part 

 developed into the apparently internal skeleton which pro- 

 tects and covers the nerve cord. 



The gizzard is that part called by cooks " the lady in the 

 lobster," and it contains firm limy bars bearing teeth which 

 clash against one another and grind the food. It should be 

 washed out and split open to see the teeth and bars. 



When all the parts of the crayfish are cleaned and laid 

 out in this way, they can be left to dry, and the whole will 

 be found exceedingly useful for reference afterwards. 



The next point is to compare the crayfish in detail with 

 the prawn. We have already noticed the similarity in 

 broad outline, but there are some interesting differences 

 in detail. Notice in the prawn the laterally compressed 

 beak, as compared with the flattened one of Nephrops; 

 this is of course associated with that difference in the shape 

 of the body which we have already noticed. The most 

 striking differences are, however, to be found in the nature 

 of the appendages. The filaments of the antennules are 

 long, and, if the prawn be a Palcemon, each antennule will 

 bear three instead of the two of Nephrops. This is a 

 point of minor importance, however, as compared with the 

 structure of the antenna. They will be found to have a 

 relatively enormous squame, or scale, as contrasted with the 

 small one of Nephrops; while the crab, again, has no trace of 

 antennal scale at all. The scale is a heritage from far-off 

 swimming ancestors, and diminishes in size as the swimming 

 power diminishes. 



The maxillipedes of the prawn (Palcemon) resemble 

 generally those of the crayfish, but the walking legs differ 

 markedly, as already noticed. They are very long and 

 slender, the first pair especially being so slender as to 

 resemble feelers rather than legs ; they are habitually carried 

 folded upon themselves, and end in minute forceps. The 

 next pair are larger and stronger and also end in forceps, 



