84 On the Nauplius Stage of Prawns. 



cystus *) the larva undergoes a metamorphosis as far as the 

 cirripede pupa-stage before it is expelled from the ovisac of 

 the parent ; and this probably (either in the ovisac or after it 

 has been liberated from it) is a stage in the progressive deve- 

 lopment of all the Suctorian tribe. 



Metschnikoff says, in the paper already alluded to, " In 

 conclusion, I must draw attention to a phenomenon which is 

 common to the Naiqylius-stage of Euphausia and Penceus ; I 

 mean the contemporaneous formation of several extremities 

 succeeding the larval swimming-feet. It is remarkable that 

 such a mode of formation is not observed in any Entomos- 

 traca which have been developed through a NaupUus-meta.- 

 morphosis. I have examined in this relation the Cirripedes 

 and Branchiopoda ; and I became convinced that in these 

 Crustacea the oral appendages are developed apart from the 

 other extremities, as has been shown by Claus for the Cope- 

 podes." 



If the oral appendages be not developed in direct sequence 

 with the anterior appendages of the head, the evidence that 

 the third pair of appendages in the Nauplius is the homo- 

 logue of the adult mandible becomes vitiated. 



Darwin has stated (p. 18, vol. i. * Monograph of the Cirri- 

 pedia ') that the cirripede in the pupa stage has no mouth. 

 " It may be called," he says, " a locomotive pujpa ; its whole 

 organization is apparently adapted for the one great end of 

 finding a proper site for its attachment and final metamor- 

 phosis." But Mr. Darwin, " underneath this slightly promi- 

 nent and closed mouth, found all the masticatory organs of a 

 cirripede in an immature condition." Later, when the animal 

 arrives at its adult stage, it is furnished with oral appen- 

 dages and uses them in eating. 



If we compare the adult Cirripede with the adult Suctorian, 

 the former, though attached to a foreign substance, has all the 

 appendages of an animal in active existence. The latter is 

 scarcely more than a sac, retaining its life apparently through 

 its parasitic union with another. Its only capability appears 

 to be the retention of a number of ova until they become 

 matured. It has no appendage, oral or otherwise. The his- 

 tory of the development of this animal is unknown to us. Of 

 what form is the male ? and when does the female become 

 impregnated ? Is it before or after it has become attached to 

 another animal ? If after, the male must be a free-swimming 

 animal ; if before, then we must assume that there is some 

 variation in its pupal condition from that of the normal cirri- 



* Proc. Roy. Soc. vol. xxiv. p. 378. 



