96 



NA TURE 



[March 25, 1909 



from the special function which it claims by its 

 title. 



It appears to be an orderly, well-written account 

 of the principles of dynamics, but rather over-burdened 

 with formulae, as, for instance, where a whole pas:e 

 of mathematics, in small print, is devoted to proving 

 that the reading of a weigh beam of an ordinary 

 platform scales is not affected by the position of the 

 load. 



Apart from these minor blemishes, and under the 

 limitations mentioned above, the work is a favourable 

 specimen of the American college text-book. 



E. G. C. 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



A Crocodile's Nest. 



The accompanving photograph was taken in the bed of 

 the river Rahad,' south-west of Gallabat, and only a few 

 miles west of the Abyssinian frontier, in May, 1907. This 

 tributary of the Blue Nile begins to come down in flood in 

 about jimc, continues to flow until the beginning of winter, 

 and after this the bed is left dry, with the exception of a 

 series of pools in the sandy river-bed. 



I came across the nest through finding a depression in 

 the sand about 4 feet above the level of a neighbouring 



pool, and a number of sinuous tracks leading down to the 

 water's edge at once suggested a crocodile's nest. The 

 hollow was about i foot deep, and the eggs were 2 inches 

 or 3 inches below the sand at the bottom of it. My guide 

 soon pulled out a number of eggs and young crocodiles, 

 which were quite willing, though not powerful enough, to 

 sample one's fingers. The find was of interest, and next 

 evening, on returning to photograph it, I was surprised 

 to find another depression about a yard further along the 

 'lank, and, covered with sand at the bottom of this, we 

 found the eggs and crocodiles shown in the picture. The 

 fggs were of the usual cylindrical shape, and about 3 inches 

 long. The crocodile on hatching is about 10 inches long, 

 perfectly formed, and makes a noise like the croaking of 

 a frog. There is generally a blood-lil<e stain about the 

 place that would correspond to the navel in higher animals. 



NO. 2056, VOL. 80] 



For the purpose of photography the eggs were taken out 

 of the sand and laid in the hollow. A crocodile is seen 

 just hatching out, and another is resting on the eggs. 

 The shells are hard, and the dark patches on some of them 

 are due to adhering sand. 



About a yard away, again, the presence of another nest 

 was made evident by the croaking of young crocodiles 

 beneath the sand, and it would appear that this enables 

 the parent to know when to release its young by excavating 

 a hollow to such a depth that only a thin covering of sand 

 is left over the eggs. 



The first nest of eggs was not counted ; a number of 

 crocodiles had already escaped into the water, about eight 

 were hatching out, and there were a good many eggs 

 besides. In the second nest there were thirty-nine eggs, 

 as the photograph shows, and the first probably contained 

 about the same number. The third nest was not un- 

 covered. There is no definite evidence for ascribing all 

 three to one parent, but in view of their being so close 

 together, and the young hatching out within two days in 

 the different nests, there is a strong presumption in favour 

 of doing so. If this is the case, the total number of eggs 

 laid by one individual can hardly have been less than a 

 hundred, and among the two batches seen only one egg 

 was found to be addled. 



I do not know whether nesting is confined to a par- 

 ticular period of the year, but in the case of a variable 

 river like the Rahad there is a considerable risk of the 

 eggs being either washed away or left at a distance by 

 the retreating water, except during the late winter and 

 spring months. 



Young crocodiles, up to about a yard in length, appear 

 to be far more active than the older ones. They leave thi; 

 pools, climb out of the river channel, and may be met at 

 a distance of fifty yards away. They are able to run at a 

 considerable pace. The older ones are generally seen float- 

 ing about or Iving on the banks close to the water. 



Khartoum, March 3. G. W. Grabham. 



A Winter Retreat for Snails. 



Some of the reaction phenomena of Helix aspersa would 

 probably account for the presence of thirty-seven specimen? 

 in an empty tea-pot as described by Prof. McKendrick in 

 Nature of March 4. 



This species is, as is well known, negatively phototropic 

 — " seeks " dark places — and is also, especially at hiberna- 

 tion, stereotropic, " attracted by surfaces." 



The empty tea-pot lay on its side by an herbaceous 

 border, where many snails would be hidden from view. 

 In November, when preparing to hibernate, these snails 

 would wander restlessly, and by the combined reactions 

 would find their way '' with mechanical certainty " into 

 the dark cavity of the tea-pot, and there come to rest. 

 The number collected together in the tea-pot would increase, 

 as, on arriving in the cavity, movement in each individual 

 would cease ; and, moreover, the individuals would cling 

 together. 



As a result, the tea-pot would act like a trap in which 

 the snails were caught, and where they would remain until 

 metabolic changes in their own bodies made them restless 

 and compelled them to move about. 



W. Hoskvns-.Abrahall. 



The Golden Fleece. 



In the review of Dr. Bowman's hook on "The .Structure 

 of the Wool Fibre, &c. " (Nature, March 4), there occurred 

 the statement that the introduction of the domestic sheep 

 into Greece was "probably enshrined in the legend of the 

 golden fleece." Strabo, however, long ago gave a plausible 

 explanation of this legend in stating (Book xi., ii, § 9): 

 " The Soanes occupy the heights of Caucasus above 

 Dioscurias " (the present Iskuria, at the mouth of the Kodor 

 in .■Xbkhasia)! ..." In their country the winter torrents 

 are said to bring down even gold, which the barbarians 

 collect in troughs pierced with holes and lined with fleeces ; 

 and hence the fable of the golden fleece." 



Felix Oswald. 



Nottingham. 



