148 HUGH WATSON. 



carnivorous form in which this has hitherto been observed is 

 Rhytida ina3qualis [Pfeiffer]} In Sele nochlamy s,~ 

 Testacella, Euglandina, Streptostyla,'^ Salasiella,* 

 and Paryphanta'^ the three visceral ganglia remain distinct, 

 and I have found that this is also the case in Natal in a and 

 in Rhytida capillacea [Fer.). In Daudebardia the 

 abdominal is fused with the right parietal ganglion.^ Lastly, 

 in the Streptaxidte, the three visceral ganglia are all more 

 or less fused to form a single mass, which is separated from 

 the pleural ganglia by long connectives.^ 



Some of the nerve-cells in the ventral group of ganglia are 

 remarkably large, especially those in the posterior parts of 

 the visceral ganglia (PI. XIV, fig. 67). One of the cells in the 

 right parietal ganglion of a specimen of Apera gibbon si 

 rubella measures "IS mm. X '143 mm., and its nucleus is no 

 less than '16 mm. x -11 mm. Fig. 69 represents a photo- 

 micrograph of a section through one of these large cells in 

 the right parietal ganglion of A. dimidia, and shows the 

 granular appearance of the large nucleus and its prominent 

 nucleolus. 



The Nerves of the Ventkal Ganglia. — The numerous 

 pedal nerves arise in an irregular longitudinal line along the 

 ventral surface of each pedal ganglion (PI. XV, figs. 73, 74), 



^ Fischer, P.. ' Joiirn. de Concliyl.' (3i-d ser.), 1873. vol. xiii. p. 8. 

 pi. iii, fig. 6. 



^Siraroth. H.. 'Festschrift Leucharts,' 1892, p. 55. pi. vi. fig. 15. 

 According to Simroth. the three visceral ganglia also remain separate 

 in Phrixolestes, but in the other genera of the Trigonochlaminse 

 they tend to fuse with one another, and even with the pleui'al ganglia 

 in Trigonochlamys itself (seeBronn's 'Klassenii. Ordn. Tier-Reichs 

 III, Gastr. Pulmonata,' 1910, p. 257, fig. 80). 



* Crosse and Fischer, ' Mission scientifique au Mexique.' 1878. pi. iv. 

 fig 5. 



■* Strebel. H , " Beitrag z. Kenntniss d. Fauna Mexik. L.-n. Si'isswasser- 

 Conchylien.' 1878, vol. iii, pi. x, fig. 7. 



" Beutler, op. cit., p. 403, pi. xxix, fig. 59. 



^ Plate, op. cit., p. 590, pi. xxxvi, figs. 94, 97. 



7 Wiegmann, F., ' Mitt. Zool. Samml. Mus. Nat. Berlin." 1898. vol. i. 

 p. 61. 



