1883.] NATURAL SCIENCES OP PHILADELPHIA. 249 



a clear mass, which takes a slight tinge when colored; this is prob- 

 ably the most active part of the cell ; in this is imbedded the large 

 oval nucleus. This nucleus is sharply demarcated and is filled 

 with a granulated matter which takes a dark color in borax car- 

 mine, as do, indeed, the nuclei of all the epidermal cells. 



These retinal cells, if they may be so called, are similar to 

 those described by P. Fraisse in 1881 (Zeit«chr. f. wiss. Zool., 

 Bd. XX v), in the very primitive eye of Patella coerulea^ the 

 principal difference being that in Patella the transparent part at 

 the top of the cell seems to be a little more extensive. This eye 

 of Patella is open, being merely an invaginated part of the epider- 

 mis, and has no lense. In Haliotis titberculafa we find an open 

 eye also, but with the addition of a very primitive lense. The 

 next higher grade of eye seems to be that of Fissur-ella rosea, in. 

 which tile eye is closed and possesses also a lense ; now in these 

 two lat'er forms, where we find a lense present, the retinal cells do 

 not possess the transparent ends as we find in Patella and Solen, . 

 but the pigment fills the upper part of the cell quite to the top. 

 This would indicate, he thinks, that the transparent part took the 

 place of a lense. 



No special nerve-fibres could be detected passing to these pig- 

 mented grooves. Nerves passing to the e\e of Patella were also 

 wanting, while, on the other hand, distinct veins were found: 

 passing to the eye of Haliotis and Fissurella. 



He further stated that this power of distinguishing a shadow 

 would be of great use to the animal in the struggle for existence. 

 The Solen lies buried perpendicularly in the sand and allows the 

 siphon to project a little above the surface. This projecting part 

 would, probably, frequently be bitten ofi' by fishes, were it not for 

 the fact that the shadow of the enemy would give warning, so 

 that the siphon could be withdrawn in time to ssxxe it fronii 

 destruction. 



Notes on Glaciers in Alaska. — Mr. Thomas Meehan remarked! 

 that on his recent visit to Alaska he noted that the numerous 

 icebergs coursing down Glacier Bay, always pursued their swiff 

 downward course towards the Pacific Ocean quite independently 

 of the rising or falling of the tide. On reflection it was evident 

 that this might be due to the greater density of the cold glacier- 

 water pressing on towards the lighter water in the Japan Sea, ., 

 which set its force against the Alaskan shores. It was, indeed, 

 incorrect to speak of a warm current flowing northwards in any 

 active sense. Warm water never flowed or circulated because it 

 was warm, but it flowed under the simple laws of gravitation — 

 the heavier body pushing the lighter out of its place, and the 

 lighter then being drawn backwards to the vacuum caused by the 

 movement of the weightier volume. The flow of a warm current 

 in tlie atmosphere or in the water must, therefore, be taken in a 

 passive and not in an active sense; and it was, therefore, to the 

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