196 



NATURE 



\yune 29, 1876 



accurately, in the fossa rhomboidea, or fourth ventricle, 

 which is remarkable for being of greater proportionate 

 size early in development, and afterwards undergoing 

 retrogression. At an early stage we only need to con- 

 ceive a slit to be made in the nerve tube at the bottom of 

 the fossa rhomboidea, in order to furnish a suitable pas- 

 sage into the alimentary canal. His first reason for 

 regarding the vertebrate mouth as a modern structure is 

 that it arises so extraordinarily late in development. The 

 embryonic body is almost completely framed, all the great 

 systems are established, the circulation is in active opera- 

 tion, while as yet there is no mouth. Again, the mouth 

 does not arise in the position in which it permanently 

 remains in the great majority. It undergoes considerable 

 shifting forwards. Only in the Selachians and Ganoids 

 does it retain its primitive situation. Moreover, the study 

 of development is steadily tending to establish the idea 

 that the mouth of Vertebrates is homodynamous with the 

 gill-clefts. It is limited, like them, by a pair of arches, 

 lies just in front of the first pair of gill-clefts, arises simul- 

 taneously with them in the embryo, and opens into the 

 alimentary canal. A glance at the ventral surface of a 

 Ray shows the likeness of the mouth to a pair of coalesced 

 gill-clefts. Consequently, it becomes probable that the 

 present mouth-opening once existed and functioned as a 

 gill-cleft ; that at a certain period in the ascending deve- 

 lopment, both the old and the new mouths supplied 

 nourishment, that the latter gained the predominance, and 

 that finally the old mouth became aborted. 



The next problem attacked is the origin of the gill- 

 clefts. A very elaborate account is given of the supposed 

 process by which the external gills and segmental organs 

 of Annelids were metamorphosed into the gills and gill- 

 clefts of Vertebrates and the skeletal elements connected 

 with them. The great difficulty which Dr. Dohrn con- 

 fesses in this matter is the connection of the inner extre- 

 mities of the segmental organs with the wall of the 

 alimentary canal. But if this be granted it is compara- 

 tively easy to understand how the shortening and widening 

 of the segmental organs might give rise to gill-cavities 

 such as those of the Selachians. The process by which 

 Dr. Dohrn conceives that the limbs of Vertebrata might 

 have been developed from two pairs of gills in Annelids 

 is a great evidence of ingenuity, though it is to be ex- 

 pected that it will be viewed rather incredulously. 



It follows from the view of the origin of Vertebrates thus 

 expounded that Amphioxus loses much of its interest, for 

 there is no place for Amphioxus among Annelids, nor 

 among the primordial Vertebrates ; it lacks almost all 

 that they possess. Yet nothing can be gained by 

 excluding Amphioxus from the Vertebrates ; for it is so 

 connected with the Cyclostome fishes that it cannot be 

 placed at any great distance from them ; while on the 

 other hand it is so related to Ascidians, that the latter 

 must be included among the Vertebrata. 



Dr. Dohrn then proceeds with along argument to show 

 that the Cyclostome fishes are degenerate from a higher 

 type of fishes, and that Amphioxus is a result of still 

 further degeneration. He shows how their mode of life 

 necessitates many of the modifications they have under- 

 gone ; and that the diversities of the details of structure 

 in Cyclostomes are inconsistent with their being viewed as 

 representing stages in upward development. Finally, the 

 larva of Ascidians is represented as a degenerate fish — a 

 degenerate Cyclostome possibly — which carries to the 

 extreme Otll the departures of the latter from the fish-type. 

 The most important element in this degeneration results 

 from the fact that Ascidians, instead of being attached to 

 fishes or to any objects from which they can derive nutri- 

 ment, are fixed to stones, plants, &q., or to such parts of 

 animals (cephalothorajc of crabs, tubes of tubicolous 

 annelids) as do not afford them nourishment. Conse- 

 quently they have lost the old mouth in the organ of 

 attachn^ent, homologous with that of all Vertebrates, and 



have developed a new one, homologous with the nasal 

 passage of Myxine. Thus we can explain the astonishing 

 fact that the mouth-opening of the Ascidian-larva has a 

 communication with the fore-wall of the so-called cere- 

 bral vesicle. It is the last vestige of the openings in the 

 nasal sacs by which the olfactory nerves entered. 



The most patent objection to Dr. Dohrn's view about 

 Amphioxus is that it fails to account for the development 

 of a many-segmented respiratory apparatus as a de- 

 generation from a higher animal with a small number of 

 gill-arches. It would appear far more reasonable to 

 suppose Amphioxus to be a degeneration from a much 

 lower elevation than the Cyclostome type, viz., from some 

 stage where the respiratory apparatus retained the multi- 

 serial character derived from its Annelid forefathers. 



The keynote of the author's reasonings is to be found 

 in the principle of Transformation of Function {Functiotis- 

 wechsel), on which he lays great stress. He states it 

 as follows : — The transfoamation of an organ happens 

 through a succession of functions being discharged by 

 one and the same organ. Each function is a resultant of 

 several components, of which one constitutes the chief or 

 primary function, while the others are lower or secondary 

 functions. Diminution of the importance of the chief 

 function with increase of the importance of a secon- 

 dary function, alters the entire resultant function ; the 

 secondary gradually rises to be the chief function, the 

 resultant function becomes different, and the consequence 

 of the whole process is the transformation of the organ. 

 This principle is considered to be a complete answer to 

 the difficulty so strongly insisted on by Mr. Mivart, the 

 incompetency of natural selection to account for the in- 

 cipient stages of subsequently useful structures. Dr. 

 Dohrn's statement of his principle does not strike us as 

 very different from Mr. Darwin's (" Origin of Species," 

 5th edition, p. 251), though a little more definitely stated. 

 Mr. Darwin says : " The same organ having performed 

 simultaneously very different functions, and then having 

 been in part or in whole specialised for one function ; and 

 two distinct organs having performed at the same time 

 the same function, the one having been perfected whilst 

 aided by the other, must often have largely facilitated 

 transitions." The illustrations given by Dr. Dohrn of the 

 steps by which the anterior extremities of Crustacea 

 became applied to mastication, how the mouth of Verte- 

 brates originated from a pair of gill-clefts, how the respi- 

 ratory apparatus of Tunicates originated from that of 

 Vertebrates, &c., are, however, exceedingly interesting. 



An English translation of Dr. Dohrn's pamphlet could 

 not fail to be serviceable to the large number of students 

 who take an interest in the genealogical problems of 

 morphology. G. T. Bettany 



MAGNETIC OBSERVATIONS IN CHINA ' 

 'T^HE first annuul report of the magnetic observations at this 

 new observatory has just reached Eufope, and it contains 

 results of considerable interest to those engaged in the study of 

 terrestrial magnetism. 



The position of Zi-ka-wei is 31° i'2' 30" N., and 8h. 5m. 45s. E. 

 of Greenwich, being rather less than four miles to the S. W. 0/ 

 Shang-Hai. The observatory is in possession of an excellent set 

 of instruments for determining the absolute values of the magnetic 

 elements, procured by the kind assistance of the Director of Kew 

 Observatory, and a set of self-recording magnetographs by Adie, 

 verified at Kew, have just been erected in a suitable building. 

 The observer, the Rev. M. Dechevrens, S.J., spent a consider- 

 able time at Stonyhurst Observatory previous to his departure 

 for China, in order to make hicnself thoroughly acquainted with 

 the methods of observation, and with the use of the instruments. 



The observations in the report extend from April 1874 to 

 March 1875, and furnish the following data for the epoch Oct. 1, 

 1874:- ■ 



■ " Observatoire Met^orologique et Magndcique de Zi-ka-wei." Chine, 

 Magn^sffle Terrestre, 1874-5. 



