MUSEUM OF COMPARATIVE ZOOLOGY. 203 



pedal ganglia originate from the ventral wall of the foot, in a region 

 and by a method corresponding to that seen in Limax maximus, as will 

 be seen by comparing his Figures 21 C to 23 with my Plate I. Figs. 5 

 and 7, and Plate IV. Fig. 57. The only important difference between 

 Vermetus and Limax lies in the fact that, in the case of the former, the 

 cells forming the ganglion remain from the beginning a more compact 

 mass than they do in the latter. 



No one except Lacaze-Duthiers ('72, pp. 456, 457) has mentioned 

 the existence of more than a single pedal commissure. He maintains 

 that there are in Lymnaeus as many as three. After speaking of the 

 cerebral ganglia as being connected by one commissure, he goes on to 

 say (p. 456), " Au contraire les ganglions pedieux ont trois commissures 

 reelles." He seems, however, uncertain as to whether the most posterior 

 ought to be considered a true commissure : " La troisieme commissure 

 merite-t-elle bien ce nom? elle est constante dans les Pulmones et se 

 presente sous la forme d'un petit nerf grele transversal naissant a peu 

 pres a la hauteur du troisieme nerf pedieux inferieur ; elle donne vers 

 son milieu naissance a un filet nerveux tres-delie, impair median que 

 Ton suit dans les tissus de la fosse pedieuse sans trop pouvoir definir et 

 limiter exactment son role/' (p. 457.) His investigations were made 

 exclusively upon the adult. 



In Limax maximus two commissures are certainly distinguishable 

 during a greater part of the embryonic life ; no trace of a third has 

 been seen. The adult has not been studied. 



None of these authors, with the exception of Sarasin, say anything 

 conclusive concerning the origin of the remaining ganglia, although 

 Salensky (86, p. 697) speaks as if the pleural ganglia of Vermetus 

 originated in the cerebro-visceral connectives, which are shown in his 

 Figures 31 B to 31 F. 



Sarasin asserts ('82, pp. 46, 47) that in Bithynia the pleural ganglia 

 originate as part of the " Sinnesplatte," from which the cerebral ganglia 

 arise, and that these ganglia, cerebral and pleural, are so closely fused 

 with each other in the later stages of development as to form on either 

 side of the body a single mass. 



I believe that they arise in Limax maximus by cell proliferations 

 from the lateral walls of the body, behind the cerebral ganglia, and just 

 above the pleural groove ; they are closely connected (not fused) with 

 the cerebral ganglia only in late stages. 



Sarasin ('82, pp. 50-52) says that the visceral ganglia in Bithynia 



