328 WILLIAM PATTEN. 



with innumerable sense-buds scattered over the skin of the 

 legs and ventral surface of the body (Fig. 3, s. b., p. 327, and 

 PI. XXIV, fig. 4) is comparable with the growth of the " supra- 

 branchial " nerve of Vertebrates. (7) Moreover, although 

 we have not determined with certainty the history of the 

 ganglia arising from the segmental sense-organs of Scorpio, 

 there is reason to suppose they represent the ganglia which, 

 according to Van Wyhe, are connected with the ventral 

 branch of cranial nerves. We should thus, in another way, 

 arrive at and confirm the conclusion of Froriep, that the 

 ventral root-ganglion is the most primitive ; for in Scorpio 

 and Limulus the segmental sense-organs and ganglia are 

 undoubtedly more primitive than the coxal ones. Beard 

 denies that there is any ganglion to the ventral root, so it is 

 difficult to determine whether the coxal sense-organs or the seg- 

 mental ones, or both, correspond to the supra-branchial sense- 

 organs described by Beard ; but for several reasons I am 

 inclined to think they are the coxal sense-organs. 



If we accept Beard's scheme of the cranial nerves, the enor- 

 mous transitory sense-organs of Limulus would come in exactly 

 the same place as the ear of Vertebrates — that is, reckoning 

 three segments to the fore-brain, on the seventh cranial 

 segment. It is also worth mentioning that the general 

 appearance of the two organs at an early stage is very much 

 alike. 



The lateral cord of ganglion-cells and nerve-fibres of Limulus 

 may be compared with the '' ganglien-zellen-straug^'' described 

 by Vejdovsky in the Oligochseta, and may be regarded as having 

 the same morphological value as the lateral cord of the central 

 nervous system. It is not improbable that the longitudinal 

 nerves of the Vertebrate head, such as that, for instance, 

 uniting the seventh and fifth nerves, are remnants of a lateral 

 nerve-cord like that in Limulus. 



IV. The Vagus Nerves of Scorpio, as I shall call them, 

 or those arising from the accessory brain, are intermediate in 



