182 



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 (Bopyrus crangorutn) ; a, upper side ; , profile ; 

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

 Bopyrus, much smaller than female;/] lower side of ditto; g, part of carapace 

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



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 



