256 



NATURE 



\July 4, 1878 



generally known. In the midst of the very beginnings of 

 life the unspeakably minute monads, as the beautiful 

 researches of Dallinger and Drysdale show, pass through 

 several stages in their individual life-history. All the 

 intervening living forms, between the monad and the man 

 pass through several stages. The " Seven Ages " attributed 

 by the poet to man are preceded by twice seven stages. 



In all times the insects showed the wonderful working 

 of the morphological force ; the poets noticed these facts 

 and sang of them ; the philosophers, also, and reasoned 

 upon them ; but it was left for us to learn that these facts 

 are not unique, but universal. Nevertheless, " the bee 

 who is small amongst those that fly, and yet her fruit is 

 the chief of sweet things," and that still smaller creature, 

 the wise-hearted ant, architect, soldier, and lawgiver ; 

 these, and the other members of the insect-class, are 

 metamorphosed openly. So, also, are the amphibia among 

 the vertebrates, for instance, the frog and the newt, whose 

 changes of fonn are so familiar to us. Still, for the most 

 part, in the vertebra ta "these things are done in a corner ;" 

 their most important changes of form are hidden from 

 unassisted vision ; to search out those secrets is the work 

 of the morphologist. 



Here, however, I will let ''that old man eloquent" — 

 Lord Bacon — speak for me ; he says that Solomon, who 

 was a great example with him, did "compile a Natural 

 History of all verdure, from the cedar upon the mountain 

 to the moss upon the wall (which is but a rudiment 

 between putrefaction and an herb), and also of all things 

 that breathe or move. Nay, the same Solomon, the king, 

 although he excelled in the glory of treasure and magni- 

 ficent buildings, of shipping and navigation, of service 

 and attendance, of fame and renown, and the like, yet he 

 maketh no claim to any of those glories, but only to the 

 glory of inquisition of truth ; for so he saith expressly, 

 ' The glory of God is to conceal a thing, but the glory of 

 the king is to find it out ; ' as if, according to the innocent 

 play of children, the Divine Majesty took delight to hide 

 his works, to the end to have them found out ; and as if 

 kings could not obtain a greater honour than to be God's 

 playfellows in that game ; considering the great com- 

 mandment of wits and means, whereby nothing needeth 

 to be hidden from them." 



It seems to us now a little thing for a great mind 

 meditating upon the form of a vertebrated animal to 

 think that the axial structures should pass into the skull, 

 when the main nervous axis so manifestly expands to 

 become the brain. Yet men were held in bondage from 

 generation to generation by the force of mere teleological 

 ideas, that do but as Bacon expresses it, " Slug and stay 

 the ship from sailing." In one place he compares people 

 who will have all these meanings and ends of things at 

 any cost, and who cannot bear to look at things in the 

 "dry light" of their efficient causes, to those low and 

 sensual people of whom one reads in holy writ, who 

 accounted the manna as poor, thin diet, and clamoured 

 for the onions, the leak, and the garlic, that flavoured the 

 flesh-pots of Egypt. Now, however, the study of struc- 

 tures, according to their mere uses, and the imagining of 

 ideal exemplars, these modes, the one imperfect and the 

 other illusory, are giving place to the observation of the 

 rise and progress in life of living creatures. 



This, rise and progress may be traced gradationally j 

 which is a tracing of form after form in the adult animals 

 existing at the present time ; a most profitable study 

 surely. To this has been added (within the last century 

 almost) the investigation of forms that have become 

 extinct; here, in "palaeontology," we come athwart forms 

 that are lower in type than their nearest relatives now 

 living. Lower, and more generalised are they : and thus 

 the mind is led to look towards the causes that have 

 operated in the extinction of the old, rough, archaic 

 forms, and the production or creation of the "lovely 

 living things ' ' that now adorn the earth. These are very 



often smaller, and, as a rule, more specialised in all respects, 

 beautified, refined, and elevated in type beyond anything 

 that could have been seen in their predecessors or pro- 

 genitors. But that which both the gradationalist and 

 palseontologist want, is a knowledge of the development 

 of the types, their life-history, indeed. 



Here is the work, this is the labour ! Our immediate 

 fathers began it ; we have entered into their labours ; but 

 our children' s children will have their hands full, not for 

 one, but for many generations. Were this done, could 

 we describe in detail the rise and progress of every part, 

 and of every organ in the structure of any form in the 

 genera, families, orders, classes, and sub-kingdoms of the 

 animal kingdom ; we might then come to some conclu- 

 sion as to the relations of these various forms, and make 

 some safe guesses as to how they have arisen. Never- 

 theless, if we cannot do all, that is no reason why we 

 should do nothing, and stand as men who cannot find 

 their hands ; the light is breaking in upon us already ; 

 albeit, the work has but just been begun. The relations 

 of living forms to each other — even in the adults — and the 

 relations of extinct to living types ; these flowers of 

 science are opening and displaying their beauties to 

 patient observers. We are now not merely considering 

 the relations of the various vertebrate classes to each 

 other, or of the various articulate, or molluscous, or 

 radiated classes, within their own special circle ; but 

 embryology is leading us to the origin, as it were, of each 

 great primary group, and of the branching off, so to speak, 

 of each great group from some common stock. 



However admirable in form and action mati now is, he 

 will soon, as a vertebrate, be ready to call the worm his 

 sister and his mother ; for his group is being set side by 

 side with the worm-group — with the living forms from 

 which sprang the " poor beetle," and the labouring ant. 

 Indeed, as seven cities claimed Homer, so several inver- 

 tebrate stocks now claim to have given birth to the noble 

 vertebrata. The noisiest claimants are the worm and the 

 rtj«rfirt«— that poor relation of the oyster; by some this 

 is thought to be madness, but there is method in it. I 

 will now quote part of an article which appeared in the 

 Nineteenth Century for December last, on " Recent 

 Science." The writer is giving an account of Prof. 

 Reichenbach' s beautiful researches into the embryology 

 of the common freshwater cray-fish, and then he goes 

 on to compare the development of the nervous axis both 

 in the invertebrata and vertebrata. 



" Until quite recently the manner in which the central 

 nervous system arises has always been considered as one 

 of the most important distinctions between vertebrate and 

 invertebrate animals. In the former, at the period when 

 the embryo is a small three-layered patch on the surface of 

 the egg, a longitudinal groove appears, the side walls of 

 which, meeting above, inclose a tube lined by the epiblast. 

 From the epiblastic cells thus shut off, the whole brain 

 and spinal cord are produced, together with the roots of 

 the cranial and spinal nerves, as the recent observations 

 of Mr. Balfour ^ and Dr. Marshall ^ have shown. In the 

 invertebrata, on the other hand, it was always supposed 

 that the nerve-cord was produced from the middle layer 

 of the embryo, or mesoblast ; but this has been shown not 

 to be the case, for it has now been proved that, in many 

 of these, the nervous system arises from a thickening of 

 epiblast, which only differs from the corresponding struc- 

 ture in vertebrata by the fact that it is not sunk in a 

 groove. But the relation, in this respect, of the two great 

 groups of the animal kingdom has never been more 

 clearly brought out than in Reichenbach' s =• paper. He 

 shows not only that the nerve-cord is a product, of the 

 epiblast, but that it arises from the cells lining an actual 



' ",0n the Development of the Fresh-water Crayfish " (Die Embryon- 

 anlage und erste Entwickelung des Flusskrebses.'') Zeitscrtft fUt ■win, 

 Zool. xxix., Bd. 2, Heft, July, 1877. , , ^ * -i o , 



* Phil. Trans., vol. clxvi., and fonrn. o/Anat.,A.vrii, la??- o^. . 



3 ycurii. of Anat. and Phys., April, 1877. 



