2/0 



ARACHNIDA XIPHOSURA 



CHAP. 



bearing appendages can be flapped to and fro, and they seem to 

 be at times held apart by the fldbellum, a spatulate process which 



Patten and Eedenbaugh regard 

 as a development of the median 

 sensory knob on the outer side 

 of the coxopodite of the last 

 pair of walking limbs. 



Limulus has no trace of 

 Malpighian tubules, structures 

 which seem often to develop 

 only when animals cease to 

 live in water and come to live 

 in air. The Xiphosura have 

 retained as organs of nitrogen- 

 ous excretion the more primi- 

 tive nephridia, or coxal glands 

 as they are called, in the 

 Arachnida. They are red- 

 brick in colour, and consist of 

 a longitudinal portion on each 



FIG. 155. Diagram of the first gill of g ^ e Q f t } le body, which gives 



Lhnnlus, from the posterior side, show- , ,1 i c 



ing the distribution of the gill-nerve to oft a lobe Opposite the base Ol 



the gill-book (about natural size). After ^ peflipalps and each of the 

 Patten and Redenbaugh. 1, Inner lobe 



of the appendage; 2, outer lobe of first three Walking - legs -- 111 



appendage; 3, median lobe of appendage; th embryo a l so o f~ the cheli- 



4, ^ill-book : 5, neural nerve ot the ninth J 



neuromere ; 6, internal branchial nerve ; cerae and last Walking legs, but 



development. A duct leads 

 from the interior of the gland and opens upon the posterior 

 face of the last pair of walking legs but one. 



The nervous system has been very fully described by Patten 

 and Kedenbaugh, and its complex nature plays a large part in the 

 ingenious speculations of Dr. Gaskell as to the origin of Verte- 

 brates. It consists of a stout ring surrounding the oesophagus 

 and a ventral nerve-cord, composed if we omit the so-called 

 fore -brain of sixteen neuromeres. The fore-lrain supplies 

 the median and the lateral eyes, and gives off a median nerve 

 which runs to an organ, described as olfactory by Patten, situated 

 in front of the chelicerae on the ventral face of the carapace. 

 Patten distinguishes behind the fore-brain a mid-brain, which 



