170 ARION ATER. 
RETRACTOR is a powerful muscle, arising from the left-side of the lung-floor, near the 
root of the tentacular retractor; it separates into two branches, a stout retractor 
muscle attached to and partially ensheathing the free-oviduct, but continued to the 
upper atrium and a somewhat more delicate branch, which is attached to the duct of 
the spermatheca, close to the vesicle. In addition there is a broad flat retractor muscle 
which also connects the atrium with the upper left side of the lung cavity. 
In full development the upper atrium is somewhat divided by a visible constric- 
tion from the lower atrium, which is closely invested by a yellow glandular pad ; 
in younger animals the lower VESTIBULE is long and slender, but does not develop 
its yellow glandular investment until maturity is approaching. 
In the black and very dark varieties, in which there is an abundance of black 
chromatophores, the proximal portions of the various organs, especially the oviduct 
and epiphallus, are liable to become more or less darkly tinged with them. 
: 
The ALIMENTARY CANAL is spir- 
ally triodromous, and shows itself to 
have been involved in the torsion which 
the whole visceral mass exhibits, the 
twisting in adults being equivalent to 
1} whorls; the STOMACH TRACT ex- 
tends most posteriorly and is separated 
by a marked constriction from the 
large brownish Crop, which is deeply 
wrinkled internally, and overspread 
externally with a network of large 
white circulatory vessels, the lacteals 
of early authors; the G:SOPHAGUS is 
purplish, with darker stripes, and from 
its origin to the nerve-ring is united 
to the buceal-mass; the SALIVARY 
GLANDS large, white, multilobed, and 
floceulent, spreading transversely and 
encircling the cesophagus like a horse- 
collar, or sometimes with ends turned 
up like a moustache; SALIVARY DUCTS 
thick ; DIGESTIVE GLAND dark brown 
or dark olive, the left lobe forming the 
end of the visceral mass, while the right 
lobe lies more anteriorly. ate 5 Fic. 197. Fic. 198. 
In young and half-grown individuals Fic. 197.—Alimentary canal of A. ater, adult x 2. 
the alimentary system quite resembles Fic. 198.—Alimentary canal of immature A. ater, 
that of A. subfuscus, showing a much showing at this stage its more intimate relationship 
shorter and apparently less complex — With 47#on sud/uscus x 3. 
arrangement than in adults, a feature due to the shorter course of its various tracts. 
The MANDIBLE or jaw is about three mill. broad and 
one mill. wide, strongly arcuate from front to back, sah 
and with a distinet fibrillar elasma, the upper half of Ree 
the jaw is imbedded in the tissues, and is of a moder- 
ately dark amber-brown, the exposed or cutting half 
is much darker or almost black, the line of separation 
of the two different shades being very perceptible and 
well defined ; the anterior surface bears from fifteen to 
eighteen strongly prominent and rounded vertical ribs 2 ; : 
which strongly crenulate the cutting edge, and also a ee or jaw 
: 2 ‘ Arion ater X 12. (Dublin 
slightly indent the upper margin. Mr. J. R. Redding). 
The LINGUAL MEMBRANE is oblong in shape, about seven mill. long. and three 
mill. in width, composed of about 160 slightly curved transverse rows of closely-set 
teeth, which do not appreciably decrease in size towards the margins ; each row is 
6) OO QAR 
Fic, 200.—Representative teeth from a transverse row of the lingual teeth of Ar‘on ater x 120. 
The animal collected at Dublin by Mr. J. R. Redding, and the palate prepared by Mr. J. W. Neville. 
54 
Nase 
