588 Transactioits. 



This string is simply a continuation of the glandular tissue ; it passes over 

 the oesophagus, under the cerebral commissure — i.e., it passes through 

 the nerve-collar. The secretion of each gland is collected by ducts which 

 ramify through the gland into a main duct. Each of these ducts (right and 

 left) leaves its respective gland near the buccal ganglion, and, passing into 

 the buccal mass close to the cerebro-buccal connective, discharges into the 

 buccal cavity near the exit of the oesophagus. The stomach is quite dif- 

 ferent from the corresponding region in Helix : there is no crop as in Helix, 

 and whereas the stomach of Helix is very small, that of Sifhonaria is very 

 large. But it may be urged that the anterior part of this region which I 

 have called stomach may correspond to the crop of Helix, especially as the 

 diameter of the tube is slightly less in the middle than at the ends. The 

 posterior end of the stomach, as I have used the term, would then correspond 

 to that of Helix. Yet for the following reasons I prefer to call it all the 

 stomach : (1) The transition externally from oesophagus to stomach is very 

 marked (Plate XXVIII, fig. 6 ; st), while it is not well marked in Helix; 

 (2) the digestive fluid is discharged into the posterior end of one large 

 chamber and is mixed with the food in that chamber, and this does not take 

 place in Helix, but the food passes out of the crop to the small stomach 

 further on, into which the digestive glands open. 



Nervous System. Fig. 5, and Plate XXVIII, fig. 6. 



The nervous system is characterized by the great concentration of its 

 ganglia in the anterior part of the body. It consists of a ring of nerve- 

 tissue surrounding the oesophagus immediately behind the buccal mass 

 at the point where the oesophagus reaches the^floor of the body-cavity 

 (fig. 5 ; Plate XXVIII, fig. 6, n). The ganglia are confined to the lateral 

 and ventral portions of the ring. In life they are of an orange colour, and 

 can thus be readily recognized. 



There is a pair of cerebral ganglia situated one on each side of the latero- 

 dorsal surface of the oesophagus, lying almost on the sides. These are put 

 into connection by a stout commissure which passes over the oesophagus 

 (fig. 5; cc). Each cerebral ganglion gives rise to six or seven nerves, which 

 innervate the cephalic region. Two of these nerves on each side go to the 

 region round the mouth, and the others are distributed to the muscles and 

 sense-organs of the floor and walls of this region, including the eyes. 



From each of these ganglia a connective goes through the muscles of 

 the buccal mass to the buccal ganglia. The buccal ganglia lie close to- 

 gether on the dorsal surface of the buccal mass u]ider the oesophagus, at 

 a point immediately behind where the latter becomes free of the buccal 

 mass (fig. 5 ; b). These ganglia are ovoid in shape, and are connected by 

 a well-defined commissure. They give ofi nerves supplying the muscles of 

 the buccal mass. 



The pleural ganglia (fig. 5 ; pi) lie very close to the cerebral, and practi- 

 cally abut upon them, so that the cerebro-pleural commissure is quite short. 

 The left pleural ganglion gives rise to a connective passing straight across 

 to the visceral ganglion, which lies very near to the right pleural ganglion, 

 being separated from the latter by a very small ganglion, probably the 

 representative of the parietal. Thus the right viscero-pleural connective 

 is very short, and consequently the whole visceral loop is likewise very 

 short, and the number of ganglia on it is reduced (fig. 5; pv, pa, v). Each 

 pleural ganglion also gives of? several nerves. From the left a large nerve 



