HARDWICKE'S SCIENCE-GOSSIP. 



scores of them the year previously, and sat near 

 together facing the wind ; just as pigeons will 

 arrange themselves on the peak of the roof of a barn 

 during a rain-storm in summer. 



In this case, these two swallows certainly became 

 thoroughly wetted, and had they been found later, 

 when the storm was over, would certainly have 

 presented the appearance of being " as wet as if they 

 had been just come out of the sea." 



How easy it is to be misled by appearances, in 

 this matter of studying bird-life ! Had I not known 

 that swallows had been flying for days before I found 

 these wet, bedraggled, storm-beaten birds, I could 

 fairly have claimed, that my own experience fully 

 confirmed the opinions of others, that swallows not 

 only migrate, but remain in mud-encased beds at the 

 bottoms of our ponds, creeks and rivers ; but until 

 swallows are first heard singing their farewell dirge, 

 as Dr. Wallerius describes, then seen to sink into the 

 mud, and are then promptly resurrected, before a 

 cloud of witnesses, it will be safe to assert that 

 what others have seen is susceptible of other expla- 

 nation than voluntary submergence in the mud of 

 our water-courses. Furthermore, it can be safely 

 asserted, I think, that bank swallows return year 

 after year to their haunts of previous summers. A 

 New York, or Connecticut, or Massachusetts colony 

 of these birds, will not reach its haunt of last summer 

 as early, as will the New Jersey colonies reach theirs. 



Although the recent observations of Mr. Scott 

 at Princeton, New Jersey, conclusively show that 

 migration at any night, when it is moonlight, 

 customarily takes place, it does not necessarily show 

 that migration at night is the common habit of all 

 birds that migrate. Indeed, it is impossible to 

 believe that however brilliant the moonlight may be, 

 any bird could distinguish, at the elevation of a 

 mile or more, the limited area of its former summer 

 haunts, the particular thicket in which it nested the 

 foregoing summer ; or, in the case of swallows, the 

 little bluff, wherein a colony had had their sub- 

 terranean summer homes. The most that can be 

 claimed, is their recognition of the particular river 

 valley wherein they have been accustomed to spend 

 the summer. Granting this, if they migrated at night, 

 then it is early in the morning after their arrival that 

 we should expect to see them, resting, in scattered 

 numbers, after their journey ; and when thus wearied 

 from a protracted flight, and damped with the dews 

 that have bathed surrounding Nature, they might 

 well present the appearance of having arisen from 

 the waters beneath, rather than fallen from the clouds 



above. 



(To be contmued.) 



Buttercup. — On December 2nd, I found a butter- 

 cup {Ranunculus repens) in flower, and it was covered 

 with ice. It was growing on an exposed bank be- 

 ween two streams. — F. II, Parrott, Aylesbury. 



MOLLUSCAN JAWS ; THEIR VARIATION 

 IN HELIX NEMORALIS, H. IIORTENSIS, 

 AND VAR. HYBRIDA. 



ANY ONE watching a snail as it crawls along, 

 cropping the alga; off the glass of a fresh-water 

 aquarium, will notice that the shorn track is distinctly 

 narrower than the foot of the animal. The lateral 

 portions of this organ describe graceful contours, 

 whilst this track has a jagged margin, and median 

 interruptions of uncropped algae. It is evident that 

 the motion of the foot has not caused that silvery 

 streak on the inner part of the glass, for, running our 

 eye along the muscular foot, from the posterior pointed 

 portion which joins the path, the so-called tail of the 

 snail, we shall see, however accomplished, whether 

 by the elongation of the anterior portion, or drawing 

 of hinder part forwards, by the alternate progressive 

 movements of the sides, or any other movement 

 common to special groups, that the use of the foot 

 is for locomotion, and that it presents no cutting 

 organ whatever. 



Anteriorly however, we find the foot of our gastro- 

 pod, if it be a Limncea, becoming very broad and 

 ending abruptly, and that there is differentiated 

 dorsally a head possessing tentacles, eyes, &c, and 

 having a mouth more or less ventral. 



Here, were we merely looking for the cause of that 

 track, our quest would end ; for the combined move- 

 ments of the head and the external organs of the 

 mouth, whilst in search of and procuring food in 

 these fields confervoid, pushed forwards by the foot, 

 give rise to the complicated tortuous Molluscan 

 tracks so common in some aquaria. A more careful 

 examination of this mouth movement through the 

 glass will reveal, in some genera more than others, a 

 dark brown or chocolate-coloured crescentic boundary, 

 the jaw, which is during life being brought constantly 

 into opposition with the more ventral portion, which 

 presents a muscular strap, on which are developed 

 hundreds of carbonate of lime denticles, the radula. 

 To the action of these organs, assisted by certain 

 muscles, is due the seizure of the food, its comminu- 

 tion and its passage to the oesophagus. The whole 

 form the buccal mass. 



In this hasty examination we have localised and 

 functionised an organ, whose action has at all times 

 excited the admiration of observers of Molluscan 

 habits. By its aid those of the snails and slugs of 

 our canals, ponds, and country lanes can be found. 

 The colour of the jaw varies from a light yellow to a 

 deep chocolate. The cuticle of the common cock- 

 roach presents the general colour sought to be 

 described. 



Generally speaking, the jaw may be said to consist 

 of a crescentic base, with or without accessory pieces, 

 on which are developed transverse ridges or ribs of 

 the same material. Neither the curvature of the 

 base, nor the number or position of the ridges is con- 



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