170 



ARION ATER. 



RETEACTOE 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 atiium is somewhat divided by a visible constric- 

 tion from the lower atrium, wliich 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 lilaok 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 J whorls ; the STOMACH TRACT ex- 

 tends most posteriorly and is separated 



by a marked constriction from the 



large brownish CEOP, which is deeply 



wrinkled internally, and overspread 



externally with a network of large 



white circulatory vessels, the lacteals 



of early authors ; the CESOPHAGUS is 



purplish, with darker stripes, and from 



its origin to the nerve-ring is united 



to the buccal-mass ; the salivary 



GLANDS large, white, multilobed, and 



flocculent, spreading transversely and 



encircling the oesophagus 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. 



In young and half -grown individuals 

 tlie alimentary system quite resembles 

 that of A. subfuscus, showing a much 

 shorter and apparently less complex 

 arrangement tlian 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, 

 and with a distinct fibrillar elasma, tlie upper half of 

 the Jaw is imbedded in the tissues, and is of a moder- 

 ately dark amber-biown, 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 ; tlie anterior .surface bears from tifteen to 

 eighteen strongly prominent and rounded vertical ribs 

 which strongly crenulate the cutting edge, and also 

 slightly indent the upper margin 



Fig. 197. 



Fig. 198. 



Fig. 197.— Alimentary canal oi A. aler, adult X 2. 



Fig. 198. — Alimentary canal of immature A . aier, 

 .showing at this stage its more intimate relationship 

 with ^ rion snbf-uscus X 3. 



■1 



Fig. 199.— Mandible or jaw 

 of Arton atey X 12. (Dublin, 

 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 tlie margins ; each row is 



Fig. 200.— Representative teeth from a transverse row of the lingual teeth o{ Anon at,-r X 120 

 Ihe animal collected at Dublin by Mr. J, R. Redding, and the palftepfe^aJed by m".J.'W Neville. 



