SMALLWOOD. — POLYCERELLA ZOOBOTRTON. 



625 



gn.opl. 



is short and narrow (5 micra long and 3 micra in diameter), while the 

 cerebro-buccal connective, arising just anterior to the cerebro-pedal 

 connective, is long and slender. Broadly joined to the ventral anterior 

 face of each cerebral 



gruvsc- 



■ co'nt.vsc. pd. 



ganglion is an olfactory 

 ganglion (Figures 9, 10, 

 gn. olf.) ; a faint constric- 

 tion is the only external 

 indication of it. The 

 olfactory ganglion is ap- 

 proximately spherical and 

 gradually tapers off into 

 the large (7 micra) nerve 

 (ji. olf.) that eventually 

 penetrates the base of the 

 rhinophore. With the 

 lateral surface of each 

 cerebral ganglion is con- 

 nected a spheroidal optic 

 ganglion {gn. ojjt.). As 

 this is sessile on the cere- 

 bral ganglion, there is no 

 conspicuous cerebro-optic 

 connective. Joined to 

 the optic ganglion is the 

 simple eye. 



The pedal ganglia lie 

 ventral, and slightly pos- 

 terior to the cerebral and 

 are somewhat smaller (22 

 by 20 by 29 micra). The 



'gn.olf. 



d 



gn.pd^^'^'^co'nt.vsc.-pdr 



Figure 10. Four camera-lucida drawings 

 (a, b, c, d) of the three pairs of gangUa in va- 

 rious positions to show their relative sizes and 

 their connectives and commissures, co'ms.cb., 

 cerebral commissure; co'^ns.pd., pedal commis- 

 sure; co'nt.vsc.-pd., viscero-pedal connective; 

 gn.cb., cerebral ganglion; gn.olf., olfactory 

 ganglion; gn.opt., optic ganglion; gn.pd., pedal 

 ganghon; gn.vsc, visceral ganglion; 7i.olf., ol- 

 factory nerve; oc, eye. 



pedal commissure (Figure 9, co'ms. pd.) is 20 micra long and 4 micra in 

 diameter ; it lies behind and ventral to the cerebro-pedal connectives. 



The visceral ganglia (Figures 9, 10) are small (10 by 10 by 10 micra) 

 in comparison with the cerebral and pedal, and lie in close contact with 

 each other. They are situated at the side of, and posterior to, the 

 esophagus back of the pedal commissures. In a frontal section is 

 found an interesting form of connection between the visceral and 

 pedal ganglia (Figure 10, a/nt. vsc.-pd.). These connectives are 15 

 micra long and 4 micra in diameter ; they form a distinct chiasma 

 with no apparent mingling of the fibres and clearly show the chiasto- 

 neuric affinities of this gasteropod. 



VOL. XLVII. — 40 



