CHAPTER X 



AEACHNIDA (CONTINUED) - DELOBRANCHIATA = MEROSTOMATA- 



XIPHOSURA 



SUB-CLASS I. DELOBBANCHIATA - MEEOSTOMATA. 



Order I. Xiphosura. 1 



I\ his recent classification of the Arachnida, Lankester" has 

 grouped the Xiphosura or King-crabs with the extinct Euryp- 

 terids or Gigantostraca under the name of Delobranchiata, better 

 known under the name Merostomata 3 of Dana. The chid' 

 character of this group, and one which differentiates it from .ill 

 the animals placed together by Lankester in the group Embolo- 

 branchiata, is that they have gills patent and exposed. The 

 Xiphosura are, in fact, with the exception of a few marine 

 the only Arachnids which now live in the sea as did their 

 the Eurypterids in Palaeozoic times. With a few fresh-water 

 exceptions, all other Arachnids have taken to life on land, and 

 with a change from water -breathing to air-breathing eanie ;) 

 change in the respiratory system, the gills becoming "lung-hunks," 

 or possibly tracheae, or disappearing altogether. 



1 Woodward, "On some Points in tin' Structure <>!' i'" 1 \i|>1i"Mii.i, liming 

 reference tn their relationship with the Eurypteridae," Quart. ./. Oeol. iii., 



1867, p. 2S, iind xxviii., 1871, ]>. 46. Milne Edward^ A.. " Recherches sur I'anat. 

 dcs Limnlcs," Ann. Sci. \t. (;"), xvii., I,s7:i, Art. 1. Lanki rti p, E. R., " l-imiilus 

 an Ararlmi,!," Quart. ./. Micr. Sci. xxi., 1881, |>. 504. Kin.^l.'y. J. S 

 Embryology of Limulus," Journ. AI<>r/>/<. vii. \>. 3;">, and \iii. ]>. 1 '.'.". 

 Kishinouye, "On the Development of Limn /its long Jowrn. 



Japan, v., lMi'2, \>. 5:5. Patten, W., and R.-ck-nbaugh, AV. A.. " Studieson 1. 

 .l<>iirn. Miii-fili. xvi., 1'JOO, ]>]>. 1, ( J1. 



- Quart. ./. .!//-/. Sci. xlviii., 1905, j>. 165. 



s s = a thigh. 



259 



