140 



MILAX GAGATES. 



Description. — Animal comparatively slender, and usually 50 mill, or more in 

 length wlien extendeil ; typically of an almost uniform black above, but in this country 

 more frequently of a drab, lavender or plumbeous-grey ; DORSAL-KEEL very prominent 

 and sharp, especially at the caudal end, where it is' abruptly angulated; it extends 

 the whole length of the back, strongly indenting the bind margin of the shield 

 wlien the anim.al is at rest, and is usually of the same or a darker colour than the 

 body; the BODY is longitudinally and regularly sulcate, the intervening spaces being 

 only slightly granulate; SHIELD or mantle am'iile, truncately rounded behind, finely 

 wrinkled and bearing a bluntly lenticular or horse-slioe shaped unpigmented sulcus, 

 which circumscribes a somewhat protuberant and sliglitly darker central ai-ea 

 beneath which the vestigial shell is lodged ; FOOT-SOLE pale, distinctly tripartite, 

 the mid -area much broader than the side-areas, and sejiarated by a deep furrow; 

 FRINGE same colour as side of sole, without lineoles, rather thick and rounded at 

 the front, defined from the sides by a deep channel ; TENTACLES moderately long and 

 granulose; lower tentacles short. Mucus thick, glutinous, and oiilonrless when iu 

 health, but when irritated or scalded tinged with pale yellow, and slightly milky 

 from the presence of innumerable minute granules of carbonate of lime. 



Shell more or less elongately oval in 

 shape, glistening white in colour, and some- 

 what convexly rounded on the upper side ; 

 APEX or nucleus subterminal and almost 

 median, encircled ^^■ith strong and regular 

 concentric lines of growth ; under-side flat, 

 or even somewhat convex owing to the 

 presence of an almost flat calcareous plate, 

 the shell thus often presenting a double 

 appearance wdien viewed laterally, simulating two shells placed one upon another. 



Length, 4i mill. ; breadth, 3 mill. 



Internally, the nervous matter is 

 closely aggregated round the throat, tlie 

 dark-grey and triangular cerebral ganglia 

 being connected by a short broad daik-grey 

 commissure; the buccal ganglia are whitish, 

 a little more than their own diameter apart, 

 and joined to the cerebral ganglia by dark- 

 grey connectives ; the SUPRA-PED.VL GLAND 

 is free, and only half the length of the body in 

 adults, and even less in immature individuals. 

 The liver is chestnut-coloured, the right lobe forming 

 visceral mass, the left is directed forwards to the KIDNEY, 

 shaped prolongation beyond the right margin of the organ. 



The ALIMENTARY CANAL shows a broad and brown ossophaous; an ample 

 brown CROP with white SALIVARY GLANDS adherent to its walls ; tlie intestinal 

 coils are triodromous, but owing to the strong spiral twisting to whicli the whole of 

 the viscera have been subjected they appear much more complex ; the second 

 intestinal tract extends beyond the termination of the stomach, and turns in the 

 caudal hibe of the liver, the rectum passing to the anal opening at the right side 

 of the boily without looping the retractor. 



The REPRODUCTIVE SYSTEM opens externally about halfway between the right 

 ommatopliore and the respiratory orifice ; the OVOTESTIS is oval and w hitish, with 

 large acini ; the DUCT becomes ample and tortuous as it nears the albumen gland, 

 where there is a well-delined VESICULA SICMINALIS; the ALBUMEN GLAND is pale 

 oehreous, gelatinous and semi-transparent; the SPERM-DUCT is of an opaque milk- 

 white colour and not well developed ; the OVIDUCT is senii-transiiarent, with a tinge 

 of blue; the FREE-OVIDUCT narrow and cylindrical; the VAS DKFERENS short, 

 enterinj; the epiphallus terminally ; the PENIS-SHEATH is small 

 and insignificant, with longitudinal ribbing, terminated distally 

 by a large and well-marked hluisli-white HPIPIIALLUS, wdiicli 

 is annularly ribbed internally, the ribs being vi.sible externally 

 as opaque- white specks; the l)asal limits are denoted exteiiorly 

 by a distinct sphincter, and interiorly by two anniilar series 

 of projecting papilla; ; the iienis-slieat'li enters the bulbous and 

 Imlging ATRIUM at the side within the protuberant jiart of 

 which, opp<isite the penial opening, there is a smooth and ploughshare- shaped 

 excitatory organ, or SARCORELUM ; the penial- retractor, which is quite slender, 



Fig. 157. — Internal RheW of JJ/. ^a^ates x 4. 

 (Christchurch, Hants, Mr. C. Ashford). 



FlG. 138.— 

 Nerve centres of 

 Milax ga^ates^ 

 showing otocysts 

 (greatly enlarged). 



the posterior end of the 

 which has a long tongue- 



FiG. 150. — S.ircoi)e- 

 liinr of MiltLX ga,^(t/cs 

 (greatly enlarged). 



