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OUR COMMON BRITISH FOSSILS. 



be stated, however, that we know little about the 

 embryology of the Trilobites. There can hardly be 

 a doubt that many of the so-called species, and even 

 genera, are larval stages in the development of the 

 same species. I have referred to the common lobster 



Fig. 149. — Parasite of Shrimp {Bo/>yrus crangorujii) ; a, upper side ; h, profile ; 

 C under side ; d, highly magnified and aborted foot ; e, upper side of male 

 Bopvrus, much smaller than female ; f, lower side of ditto ; g, part of carapace 

 of shrimp, swelling out to show presence of parasite imderneath. 



as an illustration of the clearly marked characters 

 appertaining to the various stages in the life-history of 

 the same individual. Each of these stages is accom- 

 panied by as many " moults ; " and If we reason from 

 our general experience of the embryology of the 



