9 



Class— CRUSTACEA. 



Sub-Class ClRRIPEDIA. 



Crustacea attached by the anterior end of the head, by 

 cement proceeding from a modified portion of the ovaria ; 

 archetype composed of seventeen segments, with the three 

 first of large size, and almost ahoays developed into a cara- 

 pace, not wholly exuviated, and capable of various move- 

 ments ; antenna none ; eyes rudimentary ; mouth prominent, 

 formed by the partial confluence of the labrum, palpi, man- 

 dibles, and two pairs of maxilla; thorax attached to the 

 internal sternal surface of the carapace, generally bearing 

 six pairs of captorial, biramous, multi- articulated limbs; 

 abdomen generally rudimentary ; branchice, when present, 

 attaclied to the wider sides of the carapace ; generally bi- 

 sexual, when unisexual, males epizoic on the female ; penis 

 single, generally probosciformed, seated at the posterior end 

 of the abdomen; oviducts none; metamorphoses complex. 



Within the memory of many living naturalists, Cirripedes 

 were universally looked on as belonging to the Molluscous 

 kingdom ; nor was this surprising, considering the fixed 

 condition of their shells, and the degree of external resem- 

 blance between, on the one hand, Lepas and Teredo, and 

 on the other hand, between Balanus and a Mollusc com- 

 pounded of a patella and chiton. It is remarkable that 

 this external false appearance overbore, even in the mind of 

 Cuvier, his knowledge of their internal structure, namely, 

 their lateral jaws, articulated appendages, and regular gan- 

 glionic nervous system, which now strike us as such con- 

 clusive evidence of their position in the great Articulate 

 kingdom. Straus* was, I believe, the first who, in 1819, 

 maintained that Cirripedes were most closely allied to Crus- 

 tacea. But this view was disregarded, until J. Vaughan 

 Thompson's! capital discovery, in 1830, of their metamor- 



* Memoires du Museum d'Histoire Nat., torn v, p. 381. 

 + Zoological Researches and Illustrations. 



