244 KINGSLEY. [Vol. YIII. 



by similar paired sternal arteries. A similar supra-neural 

 vessel was described long ago by Newport ('43) in several 

 Myriapods. The supra-neural vessel of the Chastopods will 

 naturally suggest itself in this connection. In the Hexapods, 

 on the other hand, the sternal arteries and the neural artery 

 have disappeared, possibly as a result of their richly developed 

 tracheal system. In Peripatus also no supra-neural vessel is 

 found, the ventral vessel first described by Balfour ('83) lying 

 in the body wall and the "blood spaces" shown in Sedg- 

 wick's monograph lying near the ventral cord, are lacunar 

 rather than arterial. 



The alimentary canal of Limulus and the Arachnids agrees 

 in the fact that nearly the whole tract is composed of stomo- 

 daeum and mesenteron while the late appearing proctodaeum is 

 short. They also agree in the metameric nature of the lobula- 

 tion of the hepatopancreas, the lobes being at first outlined by 

 the ingrowth of the mesodermic septa into the yolk. In the 

 Hexapods on the other hand the proctodaeum appears much 

 earlier and is comparatively long, at least equalling the stomo- 

 daeum in this respect. In the Crustacea on the other hand the 

 mesenteron plays but an inconspicuous part in the formation 

 of the digestive tube, it being mostly restricted to the so-called 

 liver. 



The possession of an entosternite which characterizes both 

 Limulus and the Arachnids, the structure and relationships of 

 which has already been discussed by Lankester ('84) is only 

 paralleled outside these forms in a few Crustacea (certain 

 Ostracodes, Claus, '92). 



The argument for the association of Limulus with the Crus- 

 tacea and its separation from the Arachnids, based upon the 

 possession of biramous appendages, has been accorded more 

 weight than seems justifiable. At no stage of development do 

 we find a biramous condition in the cephalothoracic appendages 

 of Limulus, while that of the abdominal appendages may prove 

 to be far different from that of the Crustacea. It appears much 

 later than in the Crustacea, is characterized by a hypertrophy 

 of the exopodite, and lacks the evident segmentation found in 

 most Crustacea. 



