March 28 1 878] 



NATURE 



419 



tially. This primordium, if it is generated within an 

 animal and remains there, until a like animal (univocum) 

 is produced, is vulgarly called a conception j if, however, 

 it :s thrust out by parturition, or if it has originated else- 

 where by chance, it is termed an ovum or vermis. I 

 think, however, that, in either case, that from which an 

 animal arises should be called primordium ; just as 

 plants produce their young from seeds ; and that all these 

 primordia are of one kind, namely, living things. 



" I find a primordium of this sort in the uterus of all 

 viviparous animals, before any foetus can be discerned. 

 In fact, there is a clear, viscid, white [colourless] fluid, like 

 the white of an egg, inclosed in a membrane, which I term 

 the egg of these animals ; and, in red-deer and fallow deer, 

 in sheep and other cloven-footed animals, it fills the whole 

 uterus and both its comua." ^ 



It will be observed that, in the foregoing passage^ 

 Harvey insists upon one main quality of the primordium, 

 namely, that it is ja. corpus similare ; or, in other words, that 

 it is relatively homogeneous ; and, in the seventy- second 

 exercise, " De humido primogenio," he insists strongly on 

 what he believes to be the fact that the embryo takes its 

 rise in a certain "humidum radicale et primigenium," 

 " simplicissimum, purissimum et sincerissimum corpus," 

 in which all the parts of the embryo are present poten- 

 tially, but not actually, and out of which they arise by a 

 gradual process of differentiation. 



" The first rudiment of the body is a mere homogeneous 

 and soft jelly, not unlike a spermatic coagulum, which, 

 becoming changed (in accordance with the law of genera- 

 tion) and at the same time split or divided into many 

 parts, as by a divine command, as we have said (let bone 

 arise here, muscle or nerve there, here viscera, there re- 

 ceptacles of excretion, &c.) out of the inorganic arises the 

 organic, out of the similar the dissimilar ; out of the one 

 and the same nature, many things of diverse and of 

 contrary natures ; not, indeed, by any transposition or 

 local motion (as when by the power of heat homogeneous 

 things unite, or heterogeneous things are separated), but 

 rather by the disaggregation of homogeneous things, than 

 by the aggregation of heterogeneous things." ^ 



In this passage, as in those in which he advocates 

 epigenesis, Harvey shows a complete grasp of the great 

 truth that development is a gradual process of change 

 from relative homogeneity to heterogeneity, put into such 

 clear light in our own time by Meckel and von Baer. 



Again, when Harvey dwells upon the close resemblance 

 of the early conditions of the higher animals, and accounts 

 for harelip as a retention of an embryonic condition, 

 we see him hovering on the brink of some of the most 

 important embryological generalisations of a century and 

 a half after his time. 



After Harvey, embryological theory distinctly' retro- 

 graded for a full century, until, in fact, a hundred and 

 eight years had elapsed, and, in 1759, Caspar Friedrich 

 Wolff published his " Theoria Generationis." In the 



' '.' De Uteri Membranis et Humoribus," Elsewhere (Exercitatio xxvi.) 

 Harvey says : — 



"Ovum itaque est corpus naturale, virtute animali praeditum : principio 

 nempe motds, transmutationis, quietis, et conservationis. Kstdenique ejus- 

 modi, ur, ablato omni impedimento, in formam animalis abitun\ni sit ; nee 

 magis naturaliter gravia omi.ia, remotis obstaculis, deorsum tendunt ; aut 

 laevia sursura moventur : quam semen et ovum in plantam aut animal, insita 

 a natuia propensione, feruiitur. tstque semen (atque etiam ovum) ejusdem 

 (ructus et finis, cujus est principium atque efficiens." 



a Ex. Ixxii. " De humido primogenio." 



interval, the great truths laid down by Harvey, that all 

 germs are homogeneous relatively to the forms to which 

 they give rise, and that all those of the higher animals, 

 at any rate, pass by epigenesis into the perfect living 

 thing — " Fabrica a parte aliqua tanquam ab origine 

 incipit : ejusque ope reliqua membra adsciscuntur : atque 

 ha;c per epigenesin fieri dicimus : sensim nempe partem 

 post partem : estque isthaee, prasaltera, proprie dicta 

 generatio" (Exercitatio xlv.); these verities, justified by 

 all our present knowledge, were ignored, and the doctrine 

 of the "pre-existence of germs" and of "evolution" took 

 their place. And so strong was the hold of the latter, 

 that even Wolff's conclusive investigations produced little 

 effect, and the full acceptance of Harvey's generalisations 

 dates from the last half-century. 



But while Harvey's views respecting the general nature 

 of the embryogenic process were as much in advance of 

 his time as were his doctrines respecting the motion of 

 the heart and the circulation of the blood, his demonstra- 

 tion of them is a failure, the phenomena being too subtle 

 and recondite for the means of investigation which he 

 possessed. 



So far as the process of fecundation is concerned, he 

 is further from the truth than were the Greeks ; for he 

 steadily denies that the male element enters into the 

 substance of the egg, or even comes into physical contact 

 with it ; and he ascribes the efficacy of the male to a 

 sort of contagion, by which the female organism is in- 

 fected, and in consequence of which, the ova, which he 

 justly declares to be formed like any other growth, acquire 

 the property of developing into embryos. 



Again, though Harvey's discovery, that the region of the 

 cicatricula in the hen's tgg is the seat of the changes 

 which give rise to the embryo, was of primary importance, 

 he has not the least notion of the real nature of the cica- 

 tricula or of its relations to the yolk. The " primigenial 

 radical humour," which he supposes to be the first com- 

 mencement of the embryo, is nothing but the amniotic fluid, 

 which is really formed long after the rudimentary body of 

 the chick has appeared. And Harvey's supposition that the 

 blood is that which is first formed and that the substance 

 of the body grows round the vessels " like a mucor or 

 fungus," is an error, which is, of course, enormous, and 

 may seem unpardonable to any one who has not tried to 

 make out the early stages of the development of the egg 

 with the naked eye, or even aided by a hand-glass. 

 It was the discovery that the rudiment of the body of 

 the chick exists in the egg, long before Harvey sup- 

 posed, that was one of the chief causes of the adoption of 

 the notion of the pre-existence of germs which led to 

 the "evolution " and " emboitement" hypotheses. Buffon, 

 in fact, went so far as to say that the chick " exists fully 

 formed {en entier) in the middle of the cicatricula when 

 the egg leaves the body of the fowl," * thereby erring as 

 far as Harvey did, but in the opposite direction. 



After due deduction is made for these errors and 

 shortcomings, however, the great merit of having been 

 the first to grasp the true principle of interpretation of 

 the process of development, must, I think, be accorded to 

 Harvey ; and if we consider the part which the study o 

 development has played, and must henceforward continue 



' Buffon, "Histoire Naturelle," t. ii., ed. 2, 1750, p. 351. 



