6 WILLIAM PATTEN. 



Attention was also called to resemblances of a more general 

 character between Vertebrates and Arachnids, such as, for 

 example, in the structure of the muscles, the nerves, and the 

 liver; in the position and the net-like structure of the sexual 

 organs; in the origin of the ova and the spermatozoa; in the 

 origin of the germ-layers, and in the general formation of the 

 embryos. 



To this formidable array of evidence I can now add the 

 following: — (1) It is possible to identify nearly all the important 

 lobes and cavities characteristic of the Vertebrate fore-brain in 

 the fore-brain of Limulus. (2) The coxal sense organs are shown 

 by conclusive experiments to be gustatory, and to correspond to 

 the supra-branchial sense organs of Vertebrates. (3) An 

 extraordinary organ has been discovered in Limulus, having 

 all the characteristic morphological features of the olfactory 

 organ in Vertebrates. It is united with olfactory lobes 

 that arise as outgrowths from the fore-brain. It consists of 

 an upright layer of epithelium containing olfactory buds similar 

 to those in the coxal (supra-branchial) sense organs. It is 

 supplied by four nerves, the median ones resembling, in histo- 

 logical structure, those of Vertebrates. One pair of these 

 nerves arises from the cerebral hemispheres, the other from the 

 optic thalami. I long ago looked for something answering to 

 the olfactory organ in Vertebrates, but finally gave up the 

 search because that part of the cephalic lobes where, as I 

 supposed, they ought to appear was invaginated, consequently 

 any sense organ derived from that region must also be invagi- 

 nated, and could not be homologous with the olfactory organ 

 of Vertebrates. 



Most of the physiological results were obtained during the 

 summer of 1892 at the United States Fish Commission 

 Laboratory at Wood's Holl, Mass., the facilities of which were 

 generously placed at my disposal by Commissioner MacDonald. 



The descriptive part of this paper deals mainly with Limulus, 

 but incidental references are made to scorpions and other 

 Arthropods. As I aim to point out resemblances between 

 Vertebrates and Arachnids, I shall not enter into histological 



