372 ARTHROrODA 



(fig. 300) is drawn out in the Lcpadidv into a long muscular stalk (lig. 115). 

 To this attached life are related all the peculiarities of structure. A lixed 

 animal has greater iteed of protection than one wliich can llee from its 

 enemies, therefore we luid right and left mande folds cai»al)le of com- 

 plete closure, like those of ait ostracode, each with two calcified plates 

 the sciila and Icrgj (figs. 115, 300. ^^ 

 5, /), the first cephalic, the other pos- 

 terior, in position. Between the 

 pairs of these is the gap through ^.^ 

 wliich the feet are protruded. 



Besides there are other calcified por- 

 tions, one of which, the lariiia (c). 

 corresponds to the hinge-line of the '* 

 ostracode and in some Le]xids is sii]i- 

 plemented by a farther unpaired piece, '' 



I'lc. 3' o. Fio. 3or. 



Fig. 300. — Bdhiiiiis Iniiiicri* aeoni barnacle U rom Lan;.j, aflcr llarwin"). Formcil of 

 rostrum, lateralia, and e.u-ina, the opcreuhnn of scuta (vl and lerua I'V 



l'"ic.. 301. — Analoiuy of Lrftos (aflor Clausl. ,i. addmlor luusele: i', carina; 

 rr, cirri l^fccO; i,^, conicnl gland; /, li\cr; o, o'. Lnar\- an<.l madnct; l\ penis; /, testis; 

 [i\ tcrgum; :', ^"as deferens. 



the rosirii))!. In the Balanidx the rostrum and carina ,are much stronger, 

 while between them other ]iaired pieces, the iatcralia, are inlerealated, Laler- 

 alia, rostrum, and carina arise from a base (nsLial]\- calc;ireous) and form a 

 cajisnle, closed above by a double val\e formed of ihc ]\iired scnla and lerna, 

 between which, when open, the animal can be seen (fig. 31)0). 



The body in both lepads and halanids has essenlially the same struc- 

 ture. It is de.xed \enlrally, so that mouth and vent arc near each otltcr, 

 and liears six pairs of feathered feet, or cirri, \\hich, when extended, 

 become widely separated a.itd lornr a most eflicicnt nteaiis of straining 

 small organisms Irom the water ;uid con\'eving thent to the mouth. These 

 feet are hiramous, with their branches ringed and thickly haired. Behiml 

 them is a rudimentary abdomen and an elongate penis; while the mouth 

 is surrounded liv a jiair of mandibles and two pairs of maxilke. 



In internal structure the most noticeable feature is that the aitimals 



