N.-1 TURli 



145 



THURSDAY, JUNE 14, 1906. 



'/•///•; RESPIRATORY SYSTEM OF VKRTE- 



BRATES. 

 l.chrhuch dcr verglcichenden mikroskopischen An- 

 atomic der Wirbeltierc. Edited by Dr. Albert 

 Oppel. Part v., Pnrielal Organ. By Dr. F. K. 

 Stiidnicka. Pp. vi + 2S4. Price S marks. Part vi., 

 .\tmungsapparat. By Dr. Albert Oppel. Pp. 

 X + S24. (Jena: Gustav Fischer, 1905.) Price 24 

 marks. 



II' any interruption should overtake the present 

 rapid growth of scientific knowledge it will not 

 be in the acquisition of new facts that the break- 

 down will occur, but in the systematisation of facts 

 already acquired by present and past generations 

 of workers. The task of systematisation, so neces- 

 sary for further progress, is in the hands of the 

 writers of text-books, but, unfortunately, the fate 

 which presides over that world wherein men of science 

 live and move has ordained that the financial success 

 of a text-book is in inverse proportion to its scientific 

 value. The general student can command with ease 

 1)(illi author and publisher, but the specialists, for 

 whom a text-book is a first necessity, find it almost 

 impossible to obtain either author or publisher. It 

 is the good fortune of those specialists who are ac- 

 tively investigating the finer structure of the verte- 

 brate body to find that, thanks to the untiring in- 

 dustry of Prof. Oppel and the enterprise of Herr 

 (nistav Fischer, the text-book they so much needed 

 has now been provided for them. In bringing to a 

 conclusion the sixth part or volume of this great 

 task, Prof. Oppel modestly consoles himself with 

 the hope that the work, to which he has devoted 

 twelve vears of his life without reward or fee, may 

 prove of use to others. It is in no niggardly spirit 

 that we in England must acknowledge the service 

 he has rendered us. 



Within the sixth volume Prof. Oppel has com- 

 pressed the results of two centuries of inquiry into 

 the minute structure of the breathing organs of 

 vertebrate animals. The facts are drawn from more than 

 900 separate publication.'; as well as from his own 

 researches, and deal with the respiratory system of 

 more than 500 species of vertebrate animals. A close 

 examination of the great mass of evidence which has 

 been thus brought together leaves one convinced that, 

 however unlike they may seem, the gill of the fish 

 and the lung of the mammal serve not only the same 

 functional purpose, but are, indeed, but modifications 

 of the self-same organ. It is now clear that in the 

 evolution of the vertebrates there has been no develop- 

 ment of a completely new organ of respiration. By 

 a process which we understand but imperfectly at 

 present, the same organ has been modified to serve 

 the same purpose in fishes, amphibians, reptiles, birds, 

 and mammals. The embryological investigations into 

 me origin of the lungs of the frog by Goetle, of the 

 fowl by Kastschenko, of the human embryo by Fol, 

 NO. 191 I, VOL. 74] 



and the later researches of Weber and Uuvigriicr. 

 leave no room to doubt the truth of that generalisa- 

 tion. 



Perhaps no two structures have engaged the specu- 

 lative f.mcy of naturalists so much as llie swim- 

 bladder of fishes and the air-sacs of birds. .\s to the 

 first, it cannot be said that the great number of ob- 

 servations which Prof. Oppel has succeeded in mass- 

 ing in his pages takes us perceptibly nearer a con- 

 ception of the true nature and origin of the swim- 

 bladder and its relationship to the vertebrate lung 

 than were the naturalists of fifty years ago. A 

 theory which regards it simply as a hydrostatic organ 

 for permitting a fish to accommodate itself to any 

 depth of water gives only a very incomplete ex- 

 planation of its presence and structure. On the other 

 hand, the nature of the air-sacs of birds is now almost 

 completely understood. When the facts grouped to- 

 gether by Prof. Oppel are considered it becomes 

 evident that in the vertebrate lung, be it of a frog, 

 of a lizard, of a bird, or of a mammal, there are three 

 distinct parts which differ in structure and in function. 

 In no vertebrate form have these three parts become 

 so highly specialised and distinctly separated as in 

 birds. The three parts are: — (i) a vascular mem- 

 brane covered by peculiar epithelium and puckered so 

 as to form alveoli (the respiratory part) ; (2) an elastic 

 chamber or series of chambers, capable of being en- 

 larged and diminished on inspiration and expiration 

 (the bellows part); (3) a series of non-collapsible tubes 

 for conveying the air to and from the air chambers 

 (the conducting part). In the avian lung the bellows 

 part has become completely separated from the re- 

 spiratory portion, and forms the air-sacs. Intermediate 

 stages in the process of separation are to be seen in 

 the lungs of reptiles. In the mammalian lung the 

 bellows part is broken up into a series of small 

 chambers throughout the whole organ, which form 

 what we in England have been in the habit of calling 

 infundibula, but which, in the more elaborate ter- 

 minology of Dr. W. S. Miller, are now demarcated 

 into vestibule, atrium, and air-sac. 



The progress of our knowledge of the minute 

 structure of the mammalian lung has been peculiarly 

 slow. In part this has been due to the elaborate 

 nomenclature employed. The same term has been 

 used to designate totally different parts, and the same 

 part has been called by several different names. Prof. 

 Oppel has done us a great service in coordinating the 

 terminology used by different investigators. It is 

 clear from the manner in which Prof. Oppel discusses 

 the question as to the nature of the epithelial cover- 

 ing of the gills that he finds it difficult to break away 

 from the tradition which has come down to us from 

 the older embrvologists — that there is a profound 

 morphological distinction between the ectodermal and 

 endodermal layers of the embryo. From the minute 

 manner in which he relates the matter it is evident 

 that he quite enjoyed the prolonged scholastic dis- 

 cussion which was first raised by .'\eby — as to whether 

 the branching of the bronchial tree was by a pro- 

 cess of dichotomy or monopody. 



11 



