PINNOTHERES, OR PEA-CRABS. 87 



on, he says, " There breed in some shells white and very 

 small crabs ; the greatest numbers are found in that species of 

 muscle which have the shell protuberant (Modioli, no doubt) ; 

 next in that of the Pinna, whose crab is named Pinnotheres. 

 They are also found in cockles and oysters. These little crabs 

 never grow in any sensible degree, and the fishermen imagine 

 that they are formed at the same time with the animal they 

 inhabit." He also gives currency to the idea, that their lives 

 are so dependent upon each other, that if the shell-fish loses 

 its little crab, they shortly afterwards perish themselves. It 

 would be idle to combat such palpable absurdities ; I shall, 

 therefore, proceed to state what appears to be matter of fact. 



The pea-crabs differ so much in the appearance of the two 

 sexes, that it is not to be wondered at if they have been consi- 

 dered as forming distinct species by some of the most acute 

 naturalists, a difference that results from that wonderful adap- 

 tation of the means to the end proposed throughout the whole 

 of the creation. The females being of a domestic and indolent 

 nature, adapted to live constantly enfolded within the soft 

 mantle of the inhabitant of the shell, are soft and globular, 

 with very short members; the males, on the contrary, being 

 erratic, and going from shell to shell, require a form and struc- 

 ture more calculated to make their way amidst banks of shells, 

 and within the opening valves of such as favour the residence 

 of their mates ; hence they are of a flatter form and firmer tex- 

 ture, of a smaller size, with long compressed members, and 

 those adapted to swimming as well as running, being densely 

 and deeply fringed ; their extreme activity, and the facility 

 with which they swim, contrasting singularly with the remark- 

 able indolence and inactivity of the other sex. This peculiar 

 structure in the males may serve to explain that passage of 

 Aristotle, from which Cuvier supposed that the Grecian philo- 

 sopher intended a species of Portunus, — " Cancelli autem qui 

 perquam exigui in pisciculis reperiuntur, pedes novissimos 

 latiusculos habent, ut ad nondum utiles sint, quasi pro pin- 

 nulis aut remis pedes haberentur." — De Part. Anim. Lib. IV. 

 cap. viii., as quoted by Cuvier, in his Diss. Crit. sur les 

 Ecrivisses. 



As the females are found with an amazing group of ova 

 under their abdominal plate, in spring, summer, and autumn, 

 it is probable that they have several successive broods ; this 

 circumstance renders it no difficult matter to select a number 



