No. I.] STUDIES ON LIMULUS. 105 



it with a pipette. The tissues to be stained were kept exposed 

 to the air and moistened from time to time with the solution. 

 This method almost invariably gave a stain of the nerves in 

 from ten minutes to one hour. 



The nerves upon the heart, pericardium, oesophagus, pro- 

 ventriculus, rectum, gills and sides of the carapace (after 

 stripping off the chitin) were easily stained by this method. 



As yet all attempts to obtain a stain of the nerves upon the 

 intestine have failed. 



I. PRELIMINARY DESCRIPTION OF THE ANATOMY OF 

 LIMULUS. 



I. External Form.^ 



The carapace of Limulus has been divided by Lankester into 

 three regions: (i) the prosomatic carapace or cephalothorax 

 (Pis. VI and VIII, Figs, i and i, pros.) ; (2) the meso-metaso- 

 matic or abdominal carapace (Pis. VI and VIII, Figs, i and 

 3, mes}i ; and (3) the postanal spine, caudal spine or telson 

 (Pis. VI-IX, Figs. 1-5, td). The terms "haemal" and 

 "neural" will be substituted for dorsal and ventral, in the 

 following descriptions. 



The cephalothorax bears upon its haemal surface two large, 

 lateral, compound eyes (Pis. VI and VII, Figs, i and 2, l.e) and 

 three simple, median eyes (Pi. VIII, Fig. 3, m.e). Early 

 observers found only two ocelli, but Patten {Quar. Jour. Micr. 

 Set., 1893) described two ectoparietal eyes, and an endoparietal 

 eye formed of two retinas fused together. 



The neural surface of the cephalothorax bears the olfactory 

 organs, mouth, nephridial openings, and seven pairs of append- 

 ages ; viz., the chelicerae, five pairs of ambulatory legs, and 

 the chilaria. 



The olfactory organs (Pis. VII and VIII, Figs. 2 and 3, 

 ol.or.) lie in the median line anterior to the chelicerae, and 

 about one-third the distance between the bases of the chelicerae 



^ For a more detailed description, see Lankester, " Limulus an Arachnid," 

 Quar. Jour. Micr. Set., and Benham, " Muscular and Endoskeletal Systems of 

 Limulus," Trans. Zool. Soc, London, 1885. 



