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AMEEICAN JOURNAL 
thè longituclinal diameter is parallel with thè axis of thè body. 
This sac is situated on thè left side, between thè lung and thè 
renai organ. Severa! largo vessels traverse thè lung, and one 
crosses it, and follows thè median line of thè gill. The smaller 
vessels could not he traced, as thè specimens had been many 
years in spirits and were extremely rigid. 
Respiratoì'y System. The lung resenibles that of Auricula, 
but is less developed than in' that genus. It is rounded tri- 
angolar, and terminates in a niultifid papilla, through which thè 
renai organ also discharges its secretions by a special duct. 
The branchiae are simply triangolar folds of thè lining mem- 
brane of thè mantle, somewhat attached to each other by a raphe, 
in thè line of which thè principal vein passes, These folds are 
more or less numerous in different individuals, apparently more 
conspicuous in thè older specimens, but by no means Constant. 
Some authors bave considered thè lungs of mollusca as invagi- 
nated gills. The present instance does not bear out thè homology. 
The gills are simple modifications of thè mantle lining, while thè 
lung is a special organ, which serves a specified purpose, and 
none other, and does not involve thè mantle lining, except as one 
of thè membranes between which tlie lung is situated. 
Reproductive System. — The genitalia bave a common opening 
into a small papilla on thè right side of thè neck, behind thè 
head. The penis is very large and stout. It is contained in a 
preputium, consisting of two spirally coiled muscular layers. 
These are continued in a kind of sac, which is reflexed anteri- 
_orly, and contains thè testicle. The lattei’ is very small and 
easily overlooked, and thè prostate is also inconspicuous. 
The ovary is large and kidney shaped. It is really doubled 
up upon itself. There is a small spirai mucus gland at thè pos- 
terior extremity, but thè duct of this gland is very long, and 
only enters thè oviduct beyond thè ovary. The latter leaves 
thè ovary with a doublé flexure, and is prolonged as a simple, 
slender tube entering thè rounded-triangular uterus by thè left 
posterior angle. The genital bladder enters on thè other side 
by a short, stout tube. The former is rounded and transversely 
ovate. The uterus is large and somewhat produced at thè pos- 
terior corners. The vagina, if we may terni it so, is moderately 
large, and opens into thè genital papilla before mentioned. The 
latter is very small in young examples. 
Nervous System. — This principally consists of a stout, ner- 
vous cullar, of ganglia united by nerve fibres, encircling thè 
oesophagus just behind thè buccal mass. More numerous fibres 
are given out below than above. One of thè former connects 
with a small accessory ganglion near thè ovary. 
