i_ 



May 25, 1S93] 



NATURE 



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pend on the numbers in which it was reproduced. Many species 

 of animals, it is needless to point out, such as rats and mice, 

 are ceaselessly persecuted by enemies, and yet survive, and from 

 time to time spread over vast areas. The lemming, notwithstand- 

 ing that thousands yearly perish by their own act, and from the 

 attacks of enemies during their migration, has not become ex- 

 tinct. Nor can I see that 2000 miles is such an "enormous 

 extent of land" for a migration to extend over, even in face of 

 carnivorous mammals and reptiles. It is at least not so great 

 as the distance covered during the migration of the South 

 American tapirs from Central Europe via Behring's Straits to 

 Brazil, the route supposed by Mr. Wallace to have been taken 

 by the ancestors of these interesting animals. 



Mr. Wallace asks, " What difficulty is there in the same or 

 closely allied species of this widespread group finding their way 

 at some remote epoch to Mauritius and the Chatham Islands, 

 and from similar causes in both islands, losing their power of 

 flight while retaining their general similarity of structure?" 

 I must reply, none ; and then ask in turn, from where did they 

 find their way? which is the point under discussion. I am con- 

 strained to believe that they came from an extensive land, 

 capable of supporting large numbers of them, which must 

 have been continuous with (as indicated by other evidence) 

 or approaching close to both regions, otherwise we have to 

 believe that this strictly Xotogsean group has "found its way" 

 across half the globe, or has arisen independently in bolh 

 regions from diflferent sections of the family — an occurrence 

 which we have no evidence to warrant our believing has ever 

 taken place. 



I am unable to speak for the present opinions of Prof. 

 Newton or his brother ; but I know of no additional evidence 

 that has come to light that is likely to have modified their 

 well-considered opinion of a few years ago. On the contrary, 

 it seems to me confirmatory of their views. 



I beg, however, to protest against the implication that I have 

 invoked this " tremendous hypothesis " to account for the dis- 

 tribution of the Aphanapteryx and FulUa I discovered. I have 

 given prominence no doubt to the valuable evidence their pre- 

 sence contributes, additional only, however, to the numerous other 

 facts I have adduced in my paper before the Royal Geographical 

 Society, in support of the theory that a land of extensive 

 dimensions — not isolated islands only as Mr. Wallace agrees to 

 — existed in the southern seas, in order to explain the distribu- 

 tion of plants and animals, unknoivn in the northirn side of the 

 equator, in regions so distant as South America, Australia, New 

 Zealand, and " Lemuria." I have, in my own opinion, adduced 

 no more cogent facts pointing in this direction than those 

 published by the late Prof. W. K. Parker, showing plainly the 

 common ancestry existing between the Notogfean (Gymnorhine) 

 crows of Australia, and the Deudrocolaptine birds of South 

 America. Their common progenitor must have occupied some 

 southern land connected with both Australia and South 

 America. 



I might adduce still other weighty examples from the 

 domain of ornithology, tending to support my opinion, which 

 have been kindly communicated to me by Dr. Bowdler Sharpe, 

 but I forbear now, as I understand that this will form the 

 subject of the second lecture of the course he is now delivering 

 on Thursday afternoons at the Royal Institution. 



104, Philbeach Gardens, May 20. HE^^RY O. FoRtiES. 



Phagocytes of Green Oysters. 



Ik your issue of May 4 you refer in a note to a sug- 

 gestion made by my friend and former pupil. Dr. Paul 

 i'elseneer that the green amoeboid cells described by me as 

 occurring on the surface of the gills of green oysters are to be 

 interpreted as out-wandered phagocytes. It is, I think, only 

 right to point out that Dr. Pelseneer (as he is careful to explain 

 ill the note published by him) has made no new observations on 

 the matter, and merely professes to give an interpretation of the 

 facts which I described in 1886 in the Quart, yoiirn. Micr. 

 Sci. in my article on green oysters. I there described and 

 figured large granular cells occurring in and upon the epithelium 

 of the gill-hlaments and regarding them as epithelial secretion- 

 cells attributed to them the active part in the elimination of the 

 blue pigment " marennin " taken in by the oyster in its food — 

 the diatom Navicula ostrcaria. At that time the general doctrine 

 of "phagocytosis" had not been so fully developed as it is 



NO. 12.30, VOL. 48] 



now seven years later. But I may say that already in 1887 one 

 of my pupils (Mr. Blundstone) had established to my satisfaction 

 the existence of extensive out-wandering of phagocytes through 

 the surface epithelium of Anodon in various regions of the body, 

 and that I was very soon led by the accumulating evidence of a 

 similar kind (e.g. Durham's observations on star-fishes) to adopt 

 the view that the large "secretion-cells" discovered by me 

 both in the epithelium of the oyster's gill and freely moving on 

 its surface, were out-wandered phagocytes. I have taught 

 this view in my lectures, and have made some further observa- 

 tions (two years ago) on similar out-wandering phagocytes in 

 other Lamellibranchs. The subject is one well worthy of 

 minute study, phagocytosis in Mollusca being as yet an unex- 

 plored ground likely to yield results of great physiological 

 importance. E. Ray Lankester. 



Oxford, May 7- 



The Conjoint Board's Medical Biolc^y. 



The pertinent remarks of L. CM. (Nature, vol. xlviii., p. 

 29), and G. B. H. (vol. xlvii,, p. 530), respecting the course of 

 elementary biology prescribed by the Conjoint Board, expresses, 

 I think, the feelings of most biologists. 



Either it is desirable, or not, that previous to entering upon 

 a course of purely medical studies the student should have a 

 training in elementary biology. The Board have decided in the 

 affirmative, and have prescribed a course as amusing as it is ab- 

 surd. It demands a practical acquaintance with the structure 

 of certain protozoa. Hydra, the leech, two or three parasitic 

 worms, a scrappy knowledge of botany, and a few generalities. 

 The insecta, Crustacea, mollusca, and the whole of the verte- 

 brata, are entirely omitted in the practical work. Under such 

 circumstances it is almost ridiculous to attempt to impart any 

 true knowledge of biology, in fact it is quite impossible to do 

 so, for in the absence of such types as the crayfish, dogfish or 

 cod, very many important morphological facts cannot be 

 illustrated. 



It would be interesting to learn the constitution of the com- 

 mittee who have drawn up this inexplicable syllabus. One really 

 cannot for a moment suppose that they are acquainted with the 

 scope and aim of present-day biological teaching, but from hazy 

 memories of their student days, and an acquaintance with 

 Ttiitia, Ascaris, and the leech, have drawn up the present 

 c )urse. The examination, I should remark, is in perfect keeping 

 with the syllabus. 



The important morphological facts to be gained by a dissec- 

 tion of the leech are probably best known to the Board. 



It is sincerely to be hoped that the matter may not be al- 

 lowed to rest here, but that some steps will be taken to impress 

 upon the Board the utter absurdity of their present syllabus and 

 mode and standard of examination, and the need for a recognized 

 course in bolh zoology and botany. 



Walter E. Collinge. 



Mason College, Birmingham, May 15. 



Vectors versus Quaternions. 



As in recent numbers of Nature my views on analysis have 

 been quoted, and not very correctly, I ask for space to state 

 them more explicitly. I see truth in the quaternion analysis 

 and in the vector analysis ; but I believe that neither the one 

 nor the other, nor the two combined, contain the whole truth. 

 The vector is an important idea, and the quaternion is an im- 

 portant idea, but there are in physical science many other 

 important ideas which call for a more direct notation. To 

 avoid any narrow hypothesis I denominated my first paper 

 "Principles of the Algebra of Physics"; but in the notice 

 which Natijre honoured it with it was printed as " Principles 

 of the Algebra of Vectors." The title I gave it indicates 

 briefly my position. I have been looking at analysis from the 

 point of view of the physicist, and one of my guiding ideas has 

 heen that the fundamental rules of analysis, instead of being 

 assumed as so many arbitrary rules of operation, should be 

 grounded on the fundamental laws of physics. 



What is the greatest want of the physicist of the present day ? 

 It is a generalised analysis which shall not contradict the 

 Cartesian analysis, but be a logical generalisation of it, which 

 shall include and harmonise such methods as the Double 

 Algebra of Argand, Cauchy, and De Morgan (an excellent pre- 

 sentation of which has recently been published by Mr. Hay- 

 ward), the method of Determinants, the Matrices of Cayley, the 



