THEIR RANK. 15 



nic, arise, and run almost parallel and under the collar 

 surrounding the oesophagus ; they are very remarkable from 

 their great size, and from forming a plexus together with 

 a large branch, arising on each side from the collar close 

 behind the supra-cesophageal ganglion, — a structure unlike 

 anything observed in other Crustaceans. The eyes, as 

 already remarked, are rudimentary, and singular from being 

 imbedded at a distance from the anterior end of the animal. 

 In the basal confluent segments of the outer maxillae there 

 are two orifices, leading into little sacks, which I believe 

 are olfactory organs : again there are two other orifices on 

 each side of the thorax, beneath the first pair of cirri, leading 

 into sacks, with a curious elastic vesicle suspended within 

 them ; and these I can hardly doubt are acoustic organs. 

 Of these orifices and organs, there is no trace in the same 

 relative positions in any known Crustacean. 



Cirripedes are ordinarily bisexual, in which they differ 

 from all Crustaceans : when the sexes are separate, the 

 males are minute, rudimentary in structure, and perma- 

 nently epizoic on the females ; to these latter facts we have 

 a partial analogy in some of the Suctorial Entomostracans ; 

 but a far closer analogy in certain Rotifers, which are 

 considered by many naturalists as Crustaceans ; but to the 

 above subject I shall almost immediately have to recur. 



The male excretory organ is probosciformed and capable 

 of the most varied movements ; it is single and medial ; it 

 is seated (in the one instance in which this point can be 

 safely judged of) at the extremity of the abdomen, and 

 therefore near the normal position of the anus ; in all 

 these respects there is a very great difference from other 

 Crustaceans, in which the male organs are laterally double, 

 and are not seated at the extremity of the abdomen. In 

 regard to the female organs, the ovarian tubes and caeca 

 inosculate together : there are no oviducts ; the ova, con- 

 nected together by membrane, and so forming the " ovi- 

 gerous lamellae," become exposed by the exuviation of the 

 lining tunic of the carapace or sack, and by the formation 

 of a new tunic on the under side of these lamellae ; a 

 process, I believe, unknown in other Crustaceans. 



The metamorphoses are highly complex. The larva in 



