ANATOMY AND LIFE HISTORY OF MOLLUSCA. 141 



cea.ses. The outer side of the testaceous fold has a narrow margin 

 like a hem, consisting of two parallel lines of dark pigment, with 

 clouds and dots of the same material between them, extending all 

 round the membrane. On its inner side it has short lines and dots 

 of brownish pigment which correspond with remarkable exactness 

 to the lines of colour on the shell. These dots when examined 

 under the microscope, are seen to be full of small and highly- 

 refractive cells. The tentacular fold bears a series of small 

 tentacles, forming a fringe all round the mantle. These tentacular 

 filaments extend slightly beyond the edge of the mantle ; they are 

 transparent, but more or less coloured with transverse lines of 

 deep olive or blackish pigment. There are from 90 to 100 of such 

 tentacles in an adult shell. They are quite distinct from the 

 branchial fringe which lies further within the cavity, leaving a 

 small space, between the gills and the muscular attachments of 

 the foot. With the exception of the narrow pigmented margin 

 on the edge of the mantle there is no pigment of a dark colour, 

 except on these tentacles ; but the origin of some of them is 

 marked for a considerable distance with a yellowish line, and the 

 space between the ophthalmic fold and the testaceous fold has a 

 slight tinge of yellow, deeper or as deep in tint as the gills. The 

 tentacles are solitary ; I have not met with double ones ; but 

 some of them have, half way from the tip, a little bulb like the 

 eye-bearing bulb on the tentacles of most of the Mollusca. A great 

 many of these tentacles are quite transparent, of a pale greenish- 

 yellow, and showing no trace of structure except with very high 

 magnifying powers. Some of them, perhaps more than half, have 

 spots and rings of very dark olive or black pigment-cells. Those 

 tentacles on which there is something like an eye-bearing bulb do 

 not, as far as I have seen, show any traces of a lens, or anything 

 indeed but a small amount of pigment, generally disposed in rings 

 round the base of the bulb. 



But what I have observed is occasionally small bulbs surrounded 

 with pigment, lying between the tentacular fold and the testaceous 

 fold, which had the shape and appearance of eyes, except that 

 what would correspond with the cornea seemed to be opaque. I 

 hardly wish to assert that they are visual organs, though they 

 may have that function and at any rate deserve further 

 examination. 



The inner surface of the mantle is slightly wrinkled, but is 

 capable of great extension to the very outward edge of the shell, 

 and of being drawn in, in curtained lobes, within the margin of 

 the foot. Frequently the tentacular fold is withdrawn between 

 the branchial and testaceous folds, so that the rounded bulbs 

 above described become completely covered, or project in a more 

 eye-like fashion. 



