48o 



NATURE 



{Sept. 30, 1875 



led to oppose exaggeration to exaggeration, we cannot 

 the less feel that there is sound sense and truth in the 

 general purport of his views. 



In the pre- Darwinian period naturalists looked upon 

 the series of classes and orders of the animal kingdom 

 as a more or less branched ascending series. The effort 

 in nearly all classifications was to distinguish the lower 

 from the higher and to place the groups in their sup- 

 posed order of merit, as competitors for the highest 

 rank of organisation. This has led— now that Darwinism 

 is accepted — to a tacit assumption that the order of 

 " degree .of organisation " which was worked out in the 

 pre-Darwinian era, is necessarily the order of historical 

 development ; that consequently the lower forms of any 

 group which are existing to day, are nearer to the ances- 

 tral forms of that group than are the more highly organised 

 forms. 



Whilst an exception has been made to this unreasoned 

 and unchallenged assumption in favour of the parasitic 

 forms for which the term " retrogressive development " 

 has been coined, it does not appear to have occurred to 

 any prominent naturalist, at any rate it has not been 

 prominently maintained, that the " retrogressive develop- 

 ment" which all so readily admit for parasites, may be a 

 very general phenomenon, as widely or more widely dif- 

 fused as that of "progressive development." To have 

 insisted on this possibility even to an excess (of which 

 more below) is the merit of Dr. Anton Dohrn. Dr. Dohrn 

 has arrived at an appreciation of the possibilities of degra- 

 dation or retrogressive development, by divesting himself 

 of all preconceived notions and of all respect for authori- 

 ties. In his pamphlet he grapples courteously, but fear- 

 lessly enough, with Von Baer, Darwin, Haeckel, Gegen- 

 baur, and for the matter of that by implication with almost 

 every zoologist of note. 



We claim for him, first of all, full liberty to do this 

 and to launch the hypothesis of general retrogressive 

 development as a competitor with that of universal pro- 

 gressive development. It requires but a few words of 

 explanation and an example, for which Dr. Dohrn has 

 selected the possible relations of the Ascidians to the 

 Vertebrata, to show that retrogressive development is not 

 only a possibility, but must be going on and has been 

 going on— on a very large scale — and in any doubtful 

 case is as much entitled to consideration as the hypothesis 

 of progressive development. A less important portion 

 of the pamphlet is that which precedes the development 

 of the author's Hypothesis of Degradation, and illustrates 

 the application of what he calls the " principle " of the 

 Succession of Functions. To put it in the form of a 

 hypothesis it comes to this : — " Organs do not arise de 

 novo in organisms, but are formed by the gradual change 

 of function and accompanying change of structure of pre- 

 existing organs." That this is true, or at any rate that it 

 is the hypothesis which, according to the " principle of 

 uniformity," must be preferred to its converse, namely, 

 " that organs are formed de novo " must be admitted by 

 everyone. In fact, most of Dr. Dohrn's readers will feel 

 that there really is not much novelty in this proposition, 

 since it is already involved in the doctrine of homologies to 

 a very large extent. Dr. Dohrn admits this in his pamph- 

 let, but we conceive that his view differs from that im- 

 plied in the generally recognised doctrine of homologies, 

 in that the latter is not aljsolute ; it would merely assert 

 that many or some organs do not arise de novo, but are 

 loimed by the gradual change of function and accom- 

 panying change of structure of pre-existing organs. Dr. 

 Dohrn raises this into a hypothesis of tmiversal appli- 

 cation, and proposes to apply it stringently in speculations 

 as to the genealogical relationships of organisms. He 

 illustrates its application in an attempt to explain the 

 genealogical affinities and mode of development of Asci- 

 dians, Amphioxus, Lampreys, and Sharks. We are very 

 much disposed to believe that here, as in his advocacy of 



the hypothesis of degradation, Dr. Dohrn has grasped 

 and emphasised a truth which has been floating before 

 the eyes of other people but has not been appreciated at 

 anything like its real importance by them. We believe 

 that the hypotheses of degradation and of continued 

 homologies put before naturalists in the present pamphlet 

 will have a very important and powerful influence on the 

 rapidly progressing reconstruction of the animal pedigree 

 with which so many zoologists are busy. 



At the same time it is necessary to point out that the par- 

 ticular speculative conclusions at which Dr. Dohrn arrives 

 as to the new Vertebrate mouth which has replaced the 

 ancestor's mouth as well as the new Ascidian mouth, 

 which has done the same thing — further, the conclusion as 

 to the secondary character of the Vertebrates' anus, and 

 the development of Vertebrate gill-slits from segment 

 organs and of Vertebrate limbs from annelidan gill- 

 supports — all this and more besides is ingenious and 

 healthy hypothesis, but has no value unless Dr. Dohrn 

 or some one else (which is not a thing he should rely 

 upon) will bring it to bear upon the facts and seek to 

 establish it by new observations. We must confess that 

 although we are inclined to entertain some of Dr. Dohrn's 

 suggestions as hypotheses, yet we feel that he has given 

 us rather a large supply, which, in justice' to his reputation 

 as an observer, he should hasten to balance by a fair 

 amount of new investigation. Such a speculation as that 

 which he gives us relative to the origin of Vertebrates,]can 

 from his hands only be regarded as a sort of programme or 

 announcement of the work which he intends to do during 

 the next decade at the Zoological Station. We shall look 

 most anxiously for the first instalment of results. 



Lastly, we shall not shrink from pointing out that Dr. 

 Dohrn urges the hypothesis of degradation to a degree 

 which would be regrettable were it quite evident that he 

 is serious and not merely anxious to engage the attention 

 of his reader by letting imagination have its full swing. 

 Supposing, says Dr. Dohrn, that the Ascidians are the 

 degenerate descendants of a half-worm- half-fish-like 

 ancestor — and the mere consideration of their individual 

 development is enough to make this probable — then we 

 have to admit an amount of degeneration which covers 

 very wide possibilities. For the compound Ascidians, 

 with their various encrusting species, are included in the 

 series ; and, moreover, many forms which have ceased 

 in their individual development to give any indication of 

 the affinities which are indicated by the larva; of other 

 forms. If so large, so abundant, and varied a group 

 can thus take its rise by degeneration, what is to prevent 

 the simpler worms from having originated in the same 

 way ? Why may not the Ccelenterata have acquired histo- 

 logical and general simplification in a parallel manner by 

 degeneration accompanying a fixed life ? And the Pro- 

 tozoa, the whole series of unicellular animals, why are 

 they not to be considered as degenerated from multi- 

 cellular forms by a process of simphfication ? In fact, in 

 a few sentences Dr. Dohrn suggests doubts which land 

 him in a theory which is almost identical with that of 

 Aristotle. 



" Thus then," he says, " the animal kingdom has quite 

 a new aspect for us when we look at it from the point of view 

 developed in this essay. Instead of having before us a 

 large mass of forms which from the first commencement 

 of organic life have made little or no progress, whilst 

 a few favoured stems have developed themselves to 

 the highest perfection, we obtain the conception of 

 one single stem, which bore within itself the germ of 

 all other higher, highest but also lowest forms, whose 

 descendants on the one hand in thought and fancy 

 embrace the universe and recognise themselves within the 

 universe as individuahties, whilst others lead a senseless 

 inert existence and give rise to the belief that a non-living 

 nature might be able now or at any time to originate such 

 things." Finally, the author argues that the development 



