May 1, 1898.] 



KNOWLEDGE. 



81 



AN ILLUSTRATED 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: MAY 1, 1893. 



CONTENTS. 



PAGE 



Moles and their Like. By R. Lydekkee, B.A.Cantab. ... 81 

 Stellar Spectra and Stellar Velocities. By Miss A. M. 



Clekke ^■^ 



Caterpillars' Dwellings— II. By E. A. Builee S5 



The Nuthatch. By Habey F. Wiihekbt 87 



Letters :— Yincext Yabdlet ; H. Beck ; T. II. Maddy ; 



.T. .T. Alexander; C. Tomlinson 88 



What is a Star Cluster P By A. C. Rantaed 90 



Science Notes 02 



Deep Sea Deposits.— Third Paper. By the Rev. H. N. 



Hutchinson, B.A., F.G.S '.»4 



On certain Low-lying Meteors. By C'haeles Tomlinson, 



F.E.S., F.C.S., &c 96 



The Face of the Sky for May. By Hebbert Sadleb, 



F.R.A.S 99 



Chess Column. By C. D. Locock, B.A.Oxon. 99 



MOLES AND THEIR LIKE. 



By R. Lydekkek, B.A.Cantab. 



IT is probably well known to most of our readers that 

 in the evolution of organized nature two great factors 

 have constantly been working against each other — 

 the one being the adherence to a particular type of 

 structure, while the other is the adaptation to a 

 special mode of life. The usual resultant of these two 

 forces has been that, in any assembly of animals specially 

 adapted for a certain peculiar kind of existence, while in- 

 ternally its different members have preserved their essential 

 structural peculiarities more or less intact, externally they 

 have become so much like one another that it often 

 requires the aid of the professed zoologist to point out their 

 essential distinctness. Perhaps in no case is this adaptive 

 similarity in external characters better displayed than 

 among certain of the smaller mammals which have taken 

 to a more or less completely subterranean burrowing 

 existence, of which the common mole is the best known 

 example. In the British Islands we have, indeed, only 

 this one creature which has adopted this particular mode of 

 life ; and it is to this animal alone that the name " mole " 

 properly belongs. Other parts of the world possess, how- 

 ever, several more or less closely allied animals to which 

 the same name must clearly be also applied. If, however, 

 we happen to have friends from the Cape, we may hear 

 them applying the name " moles " to certain burrowing 

 mammals from that district, which upon examination would 

 be found to differ essentially in structure both from the 

 ordinary moles and from one another. Then, again, if we 



were to travel in Afghanistan or some of the neighbouring 

 regions, we should meet with another mole-like burrowing 

 animal to which we should likewise feel disposed to apply 

 the same name, although it has not the most remote kin- 

 ship with our English mole. Finally, the deserts of central 

 South Australia are the dwelling-place of the recently 

 discovered " marsupial mole," which, although mole-like 

 in general form, differs from all the animals yet mentioned 

 in belonging to the marsupial order. 



We thus arrive at the conclusion that in the popular 

 sense the term " mole " now serves to indicate a number of 

 widely different animals, whose sole or chief bond of union 

 is to be found in their adaptation to a similar mode of 

 life, and their consequent assumption of a more or less 

 similar outward form. Hence, in order to avoid confusion, 

 it will be necessary to prefix the epithet " true " to those 

 species which belong to the same friendly group as the 

 " little gentleman in black velvet," while the remainder 

 must be designated by other distinctive epithets. It might 

 have been thought that such an expanded application of the 

 name " mole" was restricted to popular language. This, 

 however, is not the case, as naturalists have found it con- 

 venient to adopt the names " sand mole," " golden mole," 

 " marsupial mole," etc., as the distinctive titles of different 

 members of this purely artificial assemblage of animals; 

 and the reader will accordingly understand that when we 

 speak of " moles and their like," we merely refer to a 

 similarity in habits, and a more or less marked external 

 resemblance between the animals under consideration. 



The general bodily form of the common mole is so 

 thoroughly well known and familiar, that the term " mole- 

 like " has been introduced into zoological, if not into 

 popular, literature as a definite descriptive epithet. Since 

 it is perfectly obvious that this peculiar form is the one 

 best adapted for the needs of the creature's subterranean 

 existence, no explanation is necessary why most of the 

 other members of the assemblage have conformed more or 

 less closely to this type. We may especially notice the 

 flat, tapering, and sharp-nosed head, passing backwards 

 without any distinctly defined neck into the long and 

 cyhndrical body ; the comparative shortness of the limbs 

 and the immense strength of the front pair, which are 

 placed close to the head, and have their feet expanded into 

 broad, shovel-like organs. We shall also not fail to observe 

 the absence of any external conchs to the ears, and the 

 rudimentary condition of the deeply-buried eyes. A long 

 tail would also be u.seless to a burrowing animal, and we 

 accordingly find this appendage reduced to very small 

 dimensions ; while the close velvety hair is most admirably 

 adapted to prevent any adhesion of earthy particles during 

 the mole's subterranean journeys. Equally well-marked 

 adaptive peculiarities would also present themselves were 

 we to imdertake an examination of the mole's skeleton. 

 While the majority of the assemblage conform more or 

 less closely to the true moles in appearance, there are 

 others in which such resemblance is iDut slightly marked, 

 if apparent at all, from which we may probably infer some 

 minor difl'erences in their mode of life. 



Proceeding to the consideration of the different groups 

 of mole-like animals, it will be convenient to dinde the 

 mixed assemblage into insectivorous moles, rodent moles, 

 and marsupial moles. The term " insectivorous moles," it 

 may be premised, does not primarily indicate carnivorous 

 habits in the species thus designated, but merely refers to 

 the fact that they are members of the order Insectivora. 

 It would of course be impossible, not to say out of place, 

 to attempt a definition of that order ; but it may be men- 

 tioned that it includes small mammals, Uke shrews, moles, 

 and hedgehogs, which differ from the rodents in not pos- 



