THE VARXACLE. 



219 



l,Scalpellum rostratum. Philippines : 2, PoJlicipes comurapia, European seas : 3, 

 Tubicinella tracheal,*, attached to whales : 4, Coronula diadema, attached to 

 whales ; 5, Salanus tlntinnubulum, Atlantic : 6", section of same showing 

 animal in shell ; 6, Acasta sulcata, found in living sponges ; &, 6'', opercular 

 valves of same. 



ORDER XIII. BALANID.E.* ORDER XIV. LEPADID..t 



Thanks to Charles Darwin, Vaughan Thompson, Goodsir, and Bate, the CIRKIPEDIA, one of the 

 most aberrant groups, have now a place among the Crustacea (Figs. 40, 41). The two great divisions 

 of BALANID.E and LEPADID^E represent the condition of the adult female, or hermaphrodite ; the larvae,, 

 resembling the young of Cyclops and Cypris, being free-swimming forms, and undergoing a series of 

 metamorphosis, as do some of the highest Crustacea. 



" Almost every one," says Darwin, " who has walked over a rocky shore, knows that the 

 Barnacle, or ' acorn-shell,' is an irregular cone, formed generally of six compartments, with an orifice 

 at the top, closed by a neatly-fitted, movable 

 lid, or operculum. Within this shell the 

 animal's body is lodged, and through a slit in the 

 lid it has the power of protruding six pairs of 

 articulated cirri, or legs, and of securing by their 

 means any prey brought by the waters within 

 their reach. The basis is firmly cemented to 

 the surface of attachment. The whole shell, 

 basis, and operculum consists of the first three 

 segments of the head, modified into a singularly 

 constructed carapace, which encloses the mouth 

 and rest of the body. The anterior extremity 

 of the shell is situated in the centre of the basis, 



where, indeed, by due care, the antennae of the Fig. 40. CIHRIPEDIA. 



pupa may be always detected ; the posterior 

 extremity is directed vertically upwards." 



When the period has arrived at which 

 the young Balanus or Lepas shall assume the adult characters, it attaches itself by its antennae, 

 which are modified as cement-ducts, and by which it becomes fixed to a suitable body, organic or 

 otherwise,, and secretes a shell. 



In the one group (Balanidre) the base is fixed and immovable, save the opercular valves ; in the 

 other (Lepadidtc) the shell is supported on a peduncle more or less movable. 



" The Barnacle begins life in a form exactly like that of a young Entomosti-acous Crustacean, 

 with a broad carapace, a single eye, two pairs of antennae, three pairs of jointed, branched, and well- 

 bristled legs, and a forked tail. It casts off its skin twice, xmdergoing, especially at the second 

 moult, a considerable change of figure. At the third moult it has assumed almost the form of 

 Cypris or Cy there, being enclosed in a bivalve shell, in which the front of the head, with the 

 antennae, is greatly developed, equalling in bulk all the rest of the body. The single eye has become 

 two, which are very large, and attached to the outer arms of two bent processes, like the letters U U, 

 which are seen within the thorax (Fig. 41, c). 



" In this stage the little animal searches about for some suitable spot for permanent residence 

 a ship's bottom, a piece of floating timber, the back of a Whale or Turtle, or the solid rock. When 

 its selection is made, the two antennae, which project from the shell, pour out a glutinous gum or 

 cement, which hardens in water and firmly attaches them. Henceforth the animal is a fixture, 

 glued by the front of the head to its support. Another moult now takes place ; the bivalve shell is 

 thrown off, with the great eyes and their U-like processes, and the little Cirriped is seen in its true 

 form. It is now in effect a Stomapod Crustacean, attached by it.s antennae, the head greatly 

 lengthened (in Lepas, &c.), the carapace composed of several pieces or valves, the legs modified into 

 cirri, and made to execute their grasping movement backwards instead of forwards, and the whole 

 abdomen obliterated, or reduced to an inconspicuous rudiment." (Gosse : "Manual Marine Zoology.") 



Professor Rymer Jones observes that the food of the Cirripedia consists of various small animals, 



and nothing can be more effective or beautiful than the manner in which it obtains its prey. " Its 



food is caught in the water around them by a mechanism at once simple and elegant. Any one who 



watches the movements of a living Cirriped will at once see that its arms, with their appended cirri, 



* Latin, lalanus, an acorn. t Greek, lepas, a limpet. 



