No. I.] STUDIES ON LIMULUS. 1 25 



chilaria. The mandibles and chelae of the second, third, 

 fourth, and fifth pairs of legs, aided by the chelicerae, tear 

 the food to pieces and cram it into the mouth. The mandi- 

 bles of the sixth pair of legs crush the hard portions, and the 

 chilaria serve to push the food forward, within reach of the 

 mandibles. 



The oesophagus (Pis. VI and VIII, Figs, i, 3, and 4, oe^ 

 passes through the circum-oesophageal collar, turns anteriorly 

 neural to the endocranium, and runs forward to the muscular 

 stomach or proventriculus (Pis. VI, VIII, and IX, Figs, i, 3-5, 

 prov.), which lies at the anterior extremity of the cephalothorax. 



The provent7^icjilus (Pis. VI, VIII, and IX, Figs, i, 3-5, p7'ov.) 

 is /^shaped, and the haemal arm communicates with the intes- 

 tine by a pyloric valve, which appears as a large muscular 

 papilla at the anterior end of the intestine. The walls of the 

 oesophagus, proventriculus, and pyloric valve are very muscular, 

 and are lined with chitin, which is thrown into longitudinal 

 ridges or rugae. 



The intestine (Text-figs. 2-4 ; Pis. VI, VIlI, and IX, Figs. 

 I, 3, 4, and 6, z«/.) is a straight tube running posteriorly from 

 the proventriculus, haemal to the endocranium and ventral cord, 

 and neural to the heart. Its posterior extremity passes into a 

 short rectum or proctodaeum (PI. VIII, Figs. 3 and 4, proc). 

 Anteriorly the intestine is large, but decreases in size posteriorly. 

 The larger anterior portion receives two pairs of hepatic ducts 

 (PL VIII, Fig. 3, Ji.d."-'^), which enter at the sides of the intestine 

 nearly opposite the mouth. The walls of the intestine are sup- 

 plied with both longitudinal and circular muscle fibers, but they 

 are much thinner than the walls of the other portions of the 

 alimentary canal. 



The rectuvt or proctodaetim (PI. VIII, Figs. 3 and 4, proc) is a 

 short tube passing from the intestine to the anus. It is lined 

 like the oesophagus with chitinous rugae, and its walls are 

 supplied with well-developed muscles for the ejection of faeces. 



The amis (Pis. VI and VIII, Figs, i and 3, a.) is a longitudinal 

 slit capable of being opened and closed by the anal muscles 

 already described. 



The liver consists of a great mass of tubules ramifying over 



