72 



K, XTSTITXOUYE. 



the ainlHil:itorv legs, the four anterioi- ones of whidi are, later ,six 



joiiited, while llie la«t one is seven jointed. The la;^t anihnlatory leg 



dilfers from the other ambulatory 



leo-.s îil.r'o ])v havniij- four rod-like 



a]>]'endice.s at the ij.i.se of the ^^ixtli 



joint. The presence of these a{)- 



pendices enable:? the last anibii- 



latorv leg to serve fjr digging. 



The seventh appendage gradua.lly 



desfenerate.s fn /in the external side 



(fig. 14), leaving a small ]>roviinal 



])orlinn 'inlw ^vh!<•h he<'i)mes ihe 



nieta.stonunn ol' ilie adult. 



Tlic tippcndage:^ from tlie 

 eighth b:!ck\vai'd.-^ Ix'l.uig to ilie 

 al)domen. Tlie eiglrih pair of 

 appendage.^ bee(yme- tlie ojK'rcul um 

 (figs, 10, 12-14. 53-57, op.). 

 The riu'ht rüül left mend)ers of it 



Limulus longispina. 15. 

 (A'eutral side). 



1, Cliilaria; 7, Metasforaa ; 

 8, Opevcnliira. 



unite secondarily wirh ea'di otlier to a great extent and f )rni a single 

 jtlate (fig. = - 54, 55). The proxim:d j)ortion oi" the opercnhnn coiitaiiio 

 the me.'ohlast cells, but Hie distal ])ortion does not. Hence the 

 ])roxim:d poi'tion is verv mii''h tliicker than the distal ])oiiion (figs. 

 5.3, 54). 'I'lu' mesol)last is diffcrcntinted into muscles. Tiie Dtli-lotli 

 a.ppendagcs 1)ear the gilldamcllae. Among them the ninth ])air is 

 the earliest develojunl. fn endiryonic stages, the two lateral members 

 of the j)air are united a.t the median line only for a slight length (tigs. 

 54, 55). Like the oparcidum the a])pendage is thi«'k at the proximal 

 portion (^^j.;^. 49, 5.3, 57). Tlie epililast of the posterior side of the 

 thick portion is. invaginated by many transverse furrows. The least 



