136 MOLLUSCA. 



v 



glion, but this must be considered a secondary connection. Do 



you understand why this ganglion occupies this position? 



3. Another ganglionic mass, the abdominal ganglion, possi- 

 bly formed by the fusion of two ganglia, lies just below the exter- 

 nal opening of the kidney, where it can be seen as a brown mass, 

 through the body-wall. It lies on the elongated commissure 

 that connects the two visceral ganglia. The commissure may be 

 followed by dissection. 



The cerebral ganglia are the most centralized. Besides being 

 connected with each other by a commissure dorsal to the esopha- 

 gus, and being intimately connected with the pleural ganglia, 

 each cerebral ganglion is connected with the corresponding buc- 

 cal and pedal ganglion, and, through the pleural, with the visceral 

 ganglion. The visceral ganglia are connected with each other 

 by a long commissure on which the abdominal ganglion is placed. 

 Each pedal ganglion receives connectives from the cerebral and 

 from the pleural ganglion of the corresponding side. 



Draw figures of the nervous system and compare them with 

 the clay model. 1 



Colton: How Fulgur and Sycotypus Eat Oysters, Mussels, and Clams. 



Proc. Acad. Nat. Sci., Philadelphia, 1908. 4 

 Conklin : The Embryology of Fulgur : A Study of the Influence of Yolk on 



Development. Proc. Acad. Nat. Sci., Philadelphia, 1907. 



: The Embryology of Crepidula. Jour. Morph., 13, 1897. 



Copeland : The Olfactory Reactions and Organs of the Marine Snails, Alec- 



tripn obsoleta and Busycon canaliculatum. Jour. Exp. Zool., 25, 1918. 

 Crozier: On the Use of the Foot in Some Mollusks. Jour. Exp. Zool., 27, 



1919. .. 

 Glaser: Uber den Kannibalismus bei Fasciolaria tulipa (var. distans) und 



deren larvale Excretionsorgane. Zeit. f. wiss. Zool., 80, 1905. 

 Herrick: Mechanism of the Odontophoral Apparatus in Sycotypus canalicu- 



latus. Am. Nat., 40, 1906. 

 Olmstead: Notes on the Locomotion of Certain Bermudian Mollusks. 



Jour. Exp. Zool., 24, 1917. 



Orton: An Account of the Natural History of the Slipper-Limpet (Crepi- 

 dula fornicate). Jour. Marine Biol. Ass., 9, 1912. 

 Patten: The Embryology of Patella. Arb. Zool. Inst. Wien., 6, 1886. 



1 Instructors will find that a model prepared by sticking lumps and 

 strands of modeling clay on a cylindrical graduate, to illustrate the positions 

 of the ganglia and connectives on the esophagus, will greatly aid the 

 students. 



