88 PINNOTHERES, OR PEA-CRABS. 



of females with mature ova at any convenient time, and to pre- 

 serve them alive in sea-water for a few days, or until the ova 

 should hatch. 



METAMORPHOSIS IN PINNOTHERES. 



From several females selected and kept alive after the above 

 manner, I had the satisfaction to see the ova hatch in great 

 numbers under the form of a new kind of Zoe, differing from 

 all those previously discovered, with the front and lateral spines 

 deflected, so as to resemble a tripod. In this stage the minute 

 animals are like all the Zoea, purely natatory, disperse them- 

 selves abroad, probably undergo a further change, and may be 

 supposed to gain an easy access within the bivalve shells, 

 before they lose the power of swimming. For a considerable 

 time the young females are scarcely to be distinguished from 

 the males, and in this stage both differ so much from the 

 adult, as to render it probable that they have often been taken 

 for individuals of a different species, as would appear to have 

 been the case with Dr. Leach, whose figures of Pinnotheres 

 Latreillii, in Mai. Pod. Brit. T. XIV. f. 6, 7, 8., refer to the 

 young of his P. pisum ; this, I find, is also the opinion of 

 Montagu. 



In what the food of the Pinnotheres consists remains to be 

 determined, but must necessarily be, either the minute marine 

 animals which flow in with the current of sea-water to the 

 bronchia and mouth of the shell-fish, or the mucous secretions 

 and ejections of the animal itself. The various notions enter- 

 tained upon this subject, and upon the connexion subsisting 

 between these two animals, may serve as an amusing conclusion 

 to this outline of the natural history of the Pinnotheres, and 

 cannot fail to excite our surprise, that such fables should ever 

 have been written, quoted, and given credit to, by men of the 

 character of Cicero, Pliny, Oppian, Hasselquist, &c. 



" The Pinna," says Pliny, " is never found without its 

 companion, which is called Pinnotheres, or by others, Pinno- 

 phylax ; this is a little shrimp, in some places a small crab, 

 which bears it company in order to partake of its food. The 

 Pinna gaping wide, and showing her naked body to tempt the 

 little fishes, they soon make their approaches, and when they 

 find they have full license, grow so bold as to enter in and fill 

 it; this being seen by the guardian shrimp, by a slight nip he 

 gives the signal to the Pinna, who thereupon shuts her shell 



