114 
MONSTROSITIES — ORGANIZATION OF. 
would appear prima facie to clearly establish this latter direction as 
having now become the normal one for the coiling of the shell. 
The specimen of Plancrrhis carinafiis from Leventhorpe Pastures, 
Leeds, is an e.xample of sinistrorsity arising from a simple reversal of 
the now normal method of convolution, and nob from an atavistic 
reversion to the primitive type, as in the Planorhis ftpirorhis (f. 254); 
this is clearly attested by the position 
of the keel, which is distinctly suh-basal 
as in the pseudo-de.xtral typical form, 
and shows that the animal forming it, 
was dextrall}’ organized, as the keel 
always corrosi)onds with and indicates the 
side of the anus and other organic orifices. 
'I'lie nervous S 3 'stem oft’ei’s confirmatory evidence of the sinistra! 
character of the organization of the animal of Planorh/!^, l)j' the com- 
]>arativel 3 ' enormous development of the left visceral ganglion, which 
disparit 3 ’ in size, in comi)arisnn to the corresi)onding ganglion of the 
right .side, is mainly owing to its innervating the special .sense organ — 
Fkl 255. — Planoi'his carinatus 
monst. sintstrorsuDi Taylor x li, 
Leventhorpe Pastures, Leeds, 
Showing a simple sinistral reversal 
of the now normal pseiido-tlextral 
coiling, tlie position of the keel in- 
dicating the inmate to be de.xtrally 
organized. 
Kk;. — Nerve ring of a half-grown 
Pltinorhis comeus (L.), with cerebral com- 
missure cut and the cerebral ganglia thrown 
back, showing the sinistral organi/ation of 
l)>e animal by the comparatively verj* much 
greater development of the left \ isccral gang- 
lion (see also p. 7, lig. *5). 
Fig. 257. — Nerve ring of Limncrn percf^rn 
(Midi.), sltowing the dextral character of the 
animal by the relatively greater development 
of the right visceral ganglion (see also p. 7, f. ii). 
tbo nsphradiiim — which is situate near the re.sjtiratory erifice on the 
left side, but this organ is jilaced dextrally in the Liiniurlnw iu 
(•(iiTolation with the opjai.site arrangement of the organs of the animal. 
'I'lie character of tlie organization is further indicated by the 
position of the heart, and the situation of the reproductive and other 
orifices, the latter being always upon tbc right side of the body iu a 
dextral animal ami upon the left side of a sinistral one. The heart, 
wbicb is i)laced towards the periphery of the whorl in both dextral 
ami sinistral shells, is on the contrary normally situate on the left 
side of a dextral animal, ami on the right side of a sinistral one, but 
