1883.] NATURAL SCIENCES OF PHILADELPHIA. 231 



posterior ganglion with the oesophageal ring, I have no doubt of 

 the existence of such a connection. 



We will first consider the anterior and largest of these two 

 ganglia. From the form, position and structure I conclude that 

 this is the so-called ganglion olfactoriura. The existence of this 

 ganglion was first pointed out by Lacaze-Duthiers ^ in the Pulmo- 

 nata, but he did not suspect it to be the organ of smell. He sup- 

 posed it to be the ganglion that provided for respiration, and at 

 the same time regulated the large quantity of mucus which is 

 secreted in the region of the respiratory orifice, the moment the 

 animal is irritated at this point. Spengel,^ in his researches on 

 this organ in the Prosobranchia, believed it to be the seat of smell, 

 and gave it the name of the ganglion olfactorium. 



In Ancylus this ganglion lies on that side of the mantle which 

 forms the external wall of the branchial chamber, and almost at 

 the highest point of the chamber, namely, where the gill and 

 mantle join. 



The ganglion consists of cells with larger nuclei which are so 

 large that they almost fill out the whole cell. ThesrC nuclei take 

 a dark color when stained in picro-carmine, and are filled with a 

 large number of fine granules. No nucleolus was to be seen. The 

 whole ganglion is enveloped in a fine tunica, made up of connec- 

 tive tissue, which is continuous with the tunica that covers the 

 bundle of nerve-fibres connecting the two ganglia. 



The form of this ganglion olfactorium is in general spherical. At 

 that point where it comes in contact with the internal surface of 

 the mantle we find an invagination (PI. X, fig. 6 itif.)i so that 

 the whole ganglion has a cup-like form. This invagination I call 

 the infundibulum, because it has the form of a funnel. The 

 walls of the infundibulum are lined with cylindrical, cilated 

 epithelium, which seems to be identical to that which covers the 

 inner surface of the mantle, save that the cells and cilia of the 

 infundibulum seem to be a little longer than those of the mantle. 



^The cells stand perpendicular to the internal surface of the 

 infundibulum, and are separated from the cells of the ganglia by 

 an almost imperceptible tunica of very fine connective tissue. I 

 was unable to determine positively- whether there was direct nervous 



1 Du Syst. New d. Moll, gast., etc. 



'■' Die Geruchsorgane iind das Nervensystem der Mollusken. Zeitschr. 

 f. wiss. Zoologie, Bd. xxxv, 1881. . 



