Farnie. — The Structure of Ainphibola crenata Martyn. 79 



Tlie ganglion on the left is evidently an accessory ganglion {gnc) which 

 corresponds to that found on the visceral commissure in Ckili)ia (Lang, 

 1900, p. 220; and Naef, 1911). This accessory ganglion sends off a 

 nerve (n) which supplies the body-wall in the region of the collar. 



Between this accessory ganglion and the visceral ganglion, but nearer 

 the latter, a nerve (m) arises from the visceral commissure and supplies 

 the columellar muscle. There is no ganglion corresponding to this nerve, 

 though perhaps it arises from cells in the accessory ganglion. 



According to Pelseneer (1906), " In all Euthyneura except Actaeon, 

 Ghilina, and Latia the infra-intestinal ganglion is fused with the abdominal 

 in such a manner that the latter appears to participate in the innervation 

 of the mantle — i.e., inferior pallial lobe." Although we find that the 

 inferior pallial lobe in Amphibola is innervated by a nerve from the visceral 

 ganglion, yet serial sections across the latter give no indication of the 

 union of two such ganglia. 



In another primitive pulmonate, Latia, however, as figured by Pelseneer 

 (1906) the approximation of the ganglionic centres has not gone so far, so 

 that the infra-intestinal ganglion, although very close to the abdominal, has 

 not fused witli it. Latia, like Afnphibola, has an accessory ganglion near 

 the left pleural. The nervous system in Latia enables one to see how the 

 condition in Amphibola may have come about. 



The comparison of the nervous system of Limnaea, Chilina, and Amphi- 

 bola will show more clearly that the visceral ganglion in the last probably 

 represents the fused infra-intestinal and abdominal ganglia. 



Button's description and figure of the nervous system do not agree with 

 what I have found to be the case. He says that in addition to the cerebral 

 and pedal ganglia there is " a parieto-splanchnic system, which consists of 

 seven ganglia, three on each side, and an azygos infra-oesophageal ganglion 

 connected with the others on either side."' 



The anterior ganglion of his parieto-splanchnic system corresponds to the 

 pleural ganglion ; the posterior one to the accessory and supra-intestinal 

 respectively ; but I find no trace of the middle ganglion on either side. 

 He observes no dift'erence in size in these two ganglia, nor their asymmetry ; 

 nor does he mention any buccal ganglia. Nothing is said as to the various 

 nerves themselves. 



Sense Organs. — Tactile organs are distributed all over the surface of the 

 head and foot. This is evident by the sensitiveness exhibited when the 

 animal is touched, and also by the rich nerve-sujiply, especially in the 

 anterior margin of the head. 



A slatoci/st (or otocyst) is present on each pedal ganglion. It is an oval 

 vesicle, and contains numerous calcareous lenticular statoliths. When 

 examined fresh the statoliths oscillate in the fluid present in the vesicle. 

 These movements cease after a short time. Some of the statoliths lie on 

 the base of the nerve which leaves the statocyst. This nerve is seen 

 running close against the cerebro-pleural connective, so that one may con- 

 clude that the nerve of the statocyst comes from the cerebral ganglion. 



The osphradium, is a simple epithelial ridge on the roof of the mantle- 

 cavity close to the collar, near the pulmonary aperture (fig. 3, os). A nerve 

 can be seen supplying it from the osphradial ganglion, which is in its turn 

 innervated from the supra-intestinal ganglion. Hutton (1879) figures and 

 describes the statocyst, but makes no mention of the osphradium. 



The ej/e, as sections show, presents no peculiarity in structure ; it is 

 quite typically constructed. When a tentacle is mounted entire the eye 



