March 2, 1883.] 



SCIENCE. 



97 



oval lens lies close against the hypodermis, and can 

 be strongly stained wilh haematoxylln. From the 

 inner surface of the lens depend a cluster of pris- 

 matic cells, with nuclei in their bases, or ends away 

 from the lens. These cells fill up the interior of the 

 eye, and are enclosed in an envelope, which is fibrous, 

 pigmented, and nucleated. The fibres probably are, 

 in part at least, ramifications of the eye-nerve; the 

 envelope is separated from the inner cells (so-called 

 glasskorper) by a limiting membrane. Tliese eyes 

 conform, therefore, in their structure, with the known 

 type of annelidan eyes. The three cephalic eyes are 

 embedded in the brain. Their most remarkable 

 peculiarity is the extension of the envelope of the 

 eyes over the lenses, where it is much thickened. 

 Each eye has three lenses (in P. pictus), but other- 

 wise is similar in structure to the lateral eyes. Three 

 pear-shaped vesicles lie beside the eyes : these Meyer 

 believes to be probably otocysts. Tlie digestive 

 tract has five divisions : 1°, the mouth cavity, is a 

 rather long cylindrical tube; 2°, the pharynx, ex- 

 tends in many windings and folds to the end of the 

 fifth body-segment; it is quite muscular, and has 

 numerous peculiar glands opening into it; these two 

 parts appear to correspond to the fore-gut, while 3°, 

 the oesophagus, seems rather a portion of the mid- 

 gut, since it is lined with ciliated epithelium; 4°, the 

 largest division or stomach proper, which has two 

 ventrally placed glandular coeca at its anterior end; 

 the coeca are lined with an epithelium composed of 

 two distinct kinds of cylinder cells; the stomach has 

 an external wall of fibrous and connective tissue, 

 within which is a close network of large capillaries, 

 which gradually becomes more and more irregular 

 posteriorly ; the epithelium over the capillaries is 

 ciliated, but over each mesh there is a single cell, 

 which extends down between the vessels, and itself 

 forms a complete glandular bag, and represents a 

 hitherto unknown type of cell-form; 5°, the end- 

 gut, is very short. The vascular system is well devel- 

 oped, and is described in detail. A short account of 

 the body cavity is given ; the structure of the seg- 

 mental organs was not elucidated. The sexual organs 

 have been accurately described by Quatrefages and 

 Claparede. C. S. Minot. 



THE GLACIAL THEORY BEFORE THE 

 PHILADELPHIA ACADEMY. 



At the meeting of the Academy of natural sci- 

 ences of Philadelphia, Feb. 13, Prof. Angelo Heilprin, 

 referring to the subject of glaciation, stated that in 

 his opinion the vast ice-sheet which is generally sup- 

 posed to have covered, during the great 'ice age,' a 

 considerable portion of the northern region of the 

 European and North American continents, could not 

 have had its origin, as is maintained by most geolo- 

 gists, in a polar ice-cap; since it may be reasonably 

 doubted whether any accumulation of snow and ice 

 in the far north could ever have attained a magnitude 

 (in height) sufficient to have propelled a glacier with 

 an estimated thickness of several thousands of feet, 

 to a distance of hundreds of miles, and up mountain- 

 slopes to an elevation of five or six thousand feet. 



The height of such snow-accumulation must ne- 

 cessarily depend upon two circumstances: 1°, the 

 quantity of aqueous precipitation; and, 2°, the upjier 

 limit in the atmosphere to which clouds may attain. 

 It is well known that as a rule clouds rise highest in 

 the regions of highest temperatures, — the equatorial, 

 — where the vapor absorption by the atmosphere is 

 greatest; and, for a similar reason, higher in summer 

 than in winter. The minimum rise will therefore 



take place in the polar regions, and necessarily during 

 the polar winter. High (discharge) clouds in the ex- 

 treme north are stated by arctic explorers to be a 

 rarity, and hence precipitation in the foi'm of snow 

 must be restricted to a comparatively low atmospher- 

 ic zone. 



No great accumulation of snow can take place 

 above this zone, which must consequently be of the 

 height of the ice-cap. As a matter of fact, the officers 

 of the late arctic expedition under Sir George Nares 

 observed that the crests of the greater elevations were 

 devoid of snow, and that in the winter-months there 

 was altogether, even in tlie low lands, very little pre- 

 cipitation, heavy precipitation beginning only with 

 the spring-montlis. The greatest snow-clad elevation 

 in Greenland is Washington Land, supposed to be 

 6,000 feet, which gives origin to the great Humboldt 

 glacier. Although this peak is completely buried in 

 snow (of undetermined thickness), it may be safely 

 doubted whether, unless with a warmer climate, snow 

 of any great thickness could possibly accumulate on 

 a summit of much greater height. If not, the eleva- 

 tion, in the opinion of the speaker, was entirely in- 

 adequate to account for the phenomenon of glacial 

 propulsion southward to the extent required by geol- 

 ogists. 



Prof. H. Carvill Lewis remarked, that, notwithstand- 

 ing the difficulties in the way of a theoretical explana- 

 tion, the fact of a great continuous glacier at the 

 time of maximum glaciation seemed clearly indicated, 

 at least in America, by the numerous observations re- 

 cently made. He described the extent of the glacier 

 in America, as indicated by its terminal moraine, and 

 stated that the close similarity of its phenomena at 

 distant portions of its southern edge indicated a 

 continuous ice-sheet. The continuous motion of its 

 upper portion is shown by the uniform direction of 

 glacial striae upon elevated points. Thus the south- 

 west direction of the striae upon tlie mountain- 

 tops of northeastern Pennsylvania was identical with 

 that upon the Overlook Mountain of the Catskills 

 and that of the Laurentian of Canada. The striae 

 at lower elevations conformed more or less to the val- 

 leys, and did not indicate the general movement of 

 the ice. The thickness of the glacier increased north- 

 ward, the rate of increase diminishing as its source 

 is approached. This latter point has not heretofore 

 been appreciated, although observed some time ago 

 by Dr. Hayes in the case of the Greenland glacier. 



Recent observations by the speaker in Pennsylvania 

 had shown the glacier to be 800 feet thick at a point 

 five miles north of its extreme southern edge, and 

 2,000 feet thick at a point eight miles from its edge, 

 while it was only about 3,100 feet thiclv one hundred 

 miles farther north-east, and about 5,000 feet thick 

 three hundred miles back from its edge. The amount 

 of erosion it caused upon rock surfaces was in some 

 degree a measure of its thickness, being far greater 

 in Canada, even upon the hard Laurentian granites 

 of that region, than in Pennsylvania, where even 

 soft rocks were but slightly eroded. 



The present thickness of the glacier in central 

 Greenland was considered, and the magnitude of cer- 

 tain icebergs detached from it given. A friend of 

 the speaker had within a few months seen a floating 

 iceberg near the coast of Newfoundland which stood 

 800 feet above the water by measurement, and may 

 have been therefore nearly a mile in depth. Dr. 

 Hayes saw an iceberg aground in water nearly half a 

 mile deep. 



That the great glacier flowed up steep inclines, was 

 abundantly proven by recent observations of the 

 speaker in Pennsylvania. He instanced the striae 



