102 



Invertebrata. 



a d6ra| jsjhtiel$ armed with a strong median spine 

 (fig. 57, A) arid followed by a jointed abdomen which 

 : Jie&fs aiop appended limbs. 



A closely allied animal common on our shores 

 is the hermit crab, which protects its soft, almost 

 limbless abdomen by inserting it into the deserted 

 shell of a whelk, or other univalve mollusc. In these 



FIG. 57- 



Stages in the development of the common Shore Crab (Carcinus manas). 

 A, First or zoea stage ; B, early stage with tail ; c, D, advanced stages 

 of growth. 



the pincers are usually unequal, so that on the 

 animal being molested, one can be retracted while 

 the larger one blocks up the passage. The soft 

 abdomen acts as a sucker, whereby the hermit crab 

 retains its hold on its habitation. 



There are many varieties of form among Crustacea, 

 and those above described are among the most highly 

 organised, all having stalked eyes and ten walking 

 feet. The mantis shrimps have their thoracic limbs 

 fitted for walking, as well as the abdominal legs, so 

 that instead of ten, there are fourteen or sixteen legs. 



